Are there any maps of Kuwait before Uqair?

Yes, there were several maps that show Kuwait prior to 1922. The first map that showed a territory named "Kuwait" was the one produced by Carsten Niebuhr in Beschreibung von Arabien, published in 1772. There is an older one in the atlas of Johannes van Keulen, printed in 1753; but it uses the older name, "Grane."

Some sources say it lost as much as 2/3 of its land

This is likely referencing Harold Dickson in Kuwait and Her Neighbours (1956). Dikson, the British Political Agent to Kuwait from 1929 to 1936, remarked that at 'Uqair, in 1922, the British High Commissioner in Baghdad, Percy Cox awarded two-thirds of Kuwait to the Saudis. This caused a substantial loss of territories recognized as Kuwaiti as agreed upon in the Anglo-Ottoman Convention of 1913. Here is what the map showing Kuwait's borders according to the convention looked like. (the inner border is what we can term "Kuwait proper" whereas the outer border represent Kuwaiti territorial claims which the Ottomans and British agreed to acknowledge).