My assumption is that 'the Gospel I preach' is referring to the general set, there, rather than anything specific to Paul, but you're right that that's certainly not as clear as I'd thought. I hadn't considered that interpretation before. Thank you.
Anyway, Mikado's right that even though there can certainly be different types or levels of reading or interpretation deployed for different things we can't just write off Paul for the crime of not actually being Jesus. Saying 'it's Paul, it doesn't count' is intellectually lazy. There are any number of much more nuanced and interesting attitudes to take to the Epistles.
Well, given the stuff Paul says about women and gays, I have a hard time reconciling those passages with the overall message of Christ. "Paul doesn't count" is the position of many Scandinavian Lutherans today, but maybe we are lazy... I prefer to stick to what Christ actually said in the flesh. That is the core of the Christian message, which also makes for a significantly more tolerant religion.
