"My gospel" in the Greek text is "to euangelion…

"My gospel" in the Greek text is "to euangelion mou." Multiple Bible translations clarify that Paul is talking about his preaching assignment, not a private doctrine:
Romans 2:16
* New Living Translation (NLT): "And this is the message I proclaim—that the day is coming when God, through Christ Jesus, will judge everyone's secret life."
* The Message (MSG): "The Message from God that I proclaim through Jesus Christ takes into account all these differences."
* Good News Translation (GNT): "...According to the Good News as I proclaim it..."
2 Timothy 2:8
* New Living Translation (NLT): "Always remember that Jesus Christ, a descendant of King David, was raised from the dead. This is the Good News I preach."
* Contemporary English Version (CEV): "...He was from the family of David and was raised from death. This is the good news I preach."
* New International Version (NIV): "Remember Jesus Christ, raised from the dead, descended from David. This is my gospel," (which the NIV study tools clarify means "the Good News that I preach").
The Context
In the ancient world, a royal herald delivering a decree from a king would say, "Hear my message!" That didn't mean the herald invented the law; it meant he was the one assigned to voice it.
Paul uses "my" because he was personally entrusted with a specific stewardship to bring the one and only Gospel of Christ to the Gentiles. If he actually had a completely separate gospel from the other apostles, he would be a false prophet by his own standard in Galatians 1:8: "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed."