I don't hold to the authoritative Rome about anything.
I was posting from the history of how the Bible came to us in its present state of 66 books, which is historically accurate.
However, you did bring up two great Scriptures. The first is Peter discussing Paul's use of Scriptures. He does not state that Paul is writing the Scriptures. The second is a statement by Paul of what he considered were the Scriptures. Therefore, both verses are referring to the the writings we can find in the OT. Keep in mind that the Jews considered other writing that we do not as part of Scriptures - even to this day.
Perhaps you can find were Peter or Paul stated that what they wrote was the Scriptures. We acknowledge them as such, and I would contend that they are, but at the time of writing, they were generally letters to the churches to share with each other about matters in some instances particular to those churches, but to us providing principles for our own living. For example: Women keeping silent, learning from their husband, not trying to adorn themselves with jewelry, only the old widows and orphans would be supported by the assembly, and young women were to marry.
I am just not certain what argument you are making unless you are stating that before the Apostle John died, he sat down and made a list of what was and wasn't Scriptures and handed it to his disciples who in turn handed it down to ...
