Between 31 and 27, Octavian was technically still just one of the triumvirs, with specific constitutional powers granted by the SPQR. He spent 31 to 29 away from Italy except for one brief return, during which time he was mostly seeing to the East and disbanding the massive armies involved in the conflict. It was not until the "settlement" of 27 BCE back in Rome that his powers were redefined in terms other than that of the now-defunct triumvirate. In other words: 31 to 27 were gap years between the end of the triumvirate and the beginning of Principate. I go into more detail about this gap period in this post.