Am i wrong for arguing Norway was founded in the viking age?

Sorry for late response (I accidentally deleted my first draft).

As already suggested by several (possibly deleted) posts in this thread, such as that by /u/RenaissanceSnowblizz, how to define/ approach national identity in pre-modern Europe (prior to 1789) is certainly not so straightforward as generally assumed.

Norway never became a country before 1905

From a viewpoint of nationalism, the crucial date for Norway as a nation-state would be 1814 rather than 1905, to be sure. Then, Norway got its own first constitution as well as first university, and the Romantic Nationalism originated in Germany also used Vikings and medieval pasts to project 'their' history back to a thousand years ago in order to establish the continuity of Norway as a nation, just as France and other European national states about the same time did (Cf. Wood 2013).

In this sense, medieval kingdom of Norway cannot be the direct precursor of the 19th century Norway as nation-state, but the situation would be not so different for the case of France: The baptism of Clovis, kind of the Franks into Catholicism, would be not so a 'birth certificate' of France, as sometimes argued in 19th and 20th centuries.

On the other hand, whether Norway had really been founded by 872, especially by Harald Fairhair, as argued by OP, is almost totally different matter.

i argued that Norway was founded in the middle of the viking age 872 when Harald Hårfagre defeated the petty kings at the battle of Hafrsfjord.

Unfortunately, this assertion is problematic from a view of recent (latest half a century and little more) historians who explored the historicity of Harald Fairhair, a legendary founder of medieval Norwegian dynasty as well as the first unifying king of Norway.

As I summarize the current academic consensus before in: Did Harald Fine/Fairhair actually exist?, increasing number of scholars (especially Krag and Sverrir Jakobsson) have seen Harald in later Icelandic historical writings like Snorri primarily as a legendary figure rather than the real historical person, just as King Arthur in medieval European literature. They no longer accept the descriptions of Snorri and other kings' saga literally, and instead pay attention to trace the development of traditions in different phases. In other words, there had probably been a certain Harald called lúfa ('unkempt hair') who won the battle of Hafrsfjord in the end of the 9th century and became a 'historical' core of Harald Fairhair, but most of his other deeds, narrated in medieval sagas, were essentially later embellishments, including the famous episode of his hair as well as his moniker.

Traditions of Harald Fairhair and his dynasty, however, certainly dates back to medieval Icelandic sagas. Then, to when we can trace the provenance of the concept of medieval Norway as a kingdom, with its own dynasty?

One more relevant fact that also complicates the matter further: 'Norway' in the Viking Age had originally been a region name that encompasses a western coast of Scandinavian Peninsula. Towards the end of the Viking Age, however, the emerging polity (kingdom) and its ruler adapted its name with a political connotation.

We can also trace some different phases of this establishment of 'Norway' as a medieval kingdom, as shown below in some basic sources:

Silver coin issued by Olaf Tryggvason (c. 995): has a legend on one side (left in the picture), 'ONLAF REX NOR' in Latin. It can be translated as 'Olaf, king of Nor(way?)'. AFAIK it is the oldest contemporary evidence that any person in now Norway styled himself as a king (other evidence found only in later texts), and also, 'of Norway'.
Icelandic poet Steinn Herdísarson firstly mentions Norway as a dynastic odal (patrimony) of kin of St. Olaf (d. 1030), though not Harald Fairhair, in the skaldic poemÓláfsdrápa (‘Drápa about Óláfr’), dedicated to King Olaf Kyrre of Norway (r. 1067-93), half-nephew of St. Olaf in about 1070, as narrated as following: '(Rough translation) The battle-strong one in Trondheim, where the holy ruler rests, will refuse Sveinn his [Óláfr’s] ancestral properties; he is a mighty prince. King Óláfr will certainly grant his kin all Norway; {Úlfr’s heir} [= Sveinn (Svend Estridsen, king of the Danes)] need not make a claim there' (Óláfsdrápa, St. 7. The translation is taken from the database site).
While scholars have not reached an agreement on the exact date, at least by the later 12th century Norway was gradually regarded as a odal (patrimony) of 'Fairhair' dynasty, alleged male-line heirs of Harald Fairhair, as testified by Poem Nóregs konunga tal (Sts. 6-7): '(Rough Translation) St. 6: He did not only want to possess that which his ancestors had left him. {The ruler of the Sygnir} [NORWEGIAN KING = Haraldr] was so powerful and aggressive toward {wealth-givers} [GENEROUS MEN], that the leader possessed all the land between the Götaälv and Finnmark. He was the first to rule alone over all of Norway; St. 7: The monarch, who gave gifts, had many children who reached maturity. Therefore the kin of each ruler since is traced to Haraldr the fair-haired' (The translation of the stanzas is taken from St. 6 and St. 7 in the linked database respectively). This poem was composed at least a generation before famous royal biographies like Snorri's Heimskringla.

So, as I also discussed briefly before in: In the 12th and 13th centuries the Kingdom of Norway was wracked by a century of power-struggles. How did this instability and continual turnover of rule impact the concept of a unified "Norway" internally, and perception of the Kingdom to outsiders?, concepts of dynasty as well as a kingdom of Norway had taken root also in Norway in course of late 11th and 12th centuries, I suppose. While they did not date back to the middle of the Viking Age as OP argued, some Norwegians in the 12th century, especially those who took part in the regional assembly to accept the king, were probably familiar with these concepts.

Additional References:

Kari Ellen Gade 2009, ‘ Anonymous, Nóregs konungatal’ in Kari Ellen Gade (ed.), Poetry from the Kings’ Sagas 2: From c. 1035 to c. 1300. Skaldic Poetry of the Scandinavian Middle Ages 2. Turnhout: Brepols, pp. 761-806. https://skaldic.org/m.php?p=text&i=1035 (accessed 23 August 2021)
Kari Ellen Gade (ed.) 2009, ‘Steinn Herdísarson, Óláfsdrápa 7’ in Kari Ellen Gade (ed.), Poetry from the Kings’ Sagas 2: From c. 1035 to c. 1300. Skaldic Poetry of the Scandinavian Middle Ages 2. Turnhout: Brepols, pp. 373-4.

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Krag, Claus. Norges historie fram til 1319. Oslo: Universitetsforlag, 2000.
Myhre, Jan E. 'The "Decline of Norway": Grief and Fascination in Norwegian Historiography on the Middle Ages'. In: The Uses of the Middle Ages in Modern European States: History, Nationhood and the Search for Origins, ed. R. J. W. Evans & Guy P. Marchal, pp. 19-30. Basingstoke: Palgrave, 2011.
Wood, Ian. The Modern Origins of the Early Middle Ages. Oxford: OUP, 2013.