Peter referred to Paul's writings as scripture.
Possibly, but that understanding is by no means definite.
Peter was making a point about how people use the complexity of Paul’s letters to twist their meaning, as also they do with other complex scriptures, and that thought is the main message there.
No he referred to his writings as writings, that is what the Greek word scripture means. It was only after the Catholic Church ordered the canon that scripture came to mean the Bible. Common mistake among non/anti-Catholics and the illiterate.