Did Peter ever agree that Paul's gospel was right?
Yes. Scripture records Peter calling Paul "our beloved brother" and acknowledging the wisdom given to Paul. Peter still had difficulty understanding some things, yet he had to agree that Paul was on the right track. Peter's struggle came from being steeped in Judaism and legalism.
Les explains that Peter's later words refer to Paul as "our beloved brother" and speak of the wisdom given to Paul, whose epistles cover Romans through Hebrews. Even thirty years afterward, Peter still had problems and some things were hard to understand, but he had to agree Paul was on the right track. Les says Peter struggled because he was steeped in Judaism and legalism, and coming out from legalism into grace is hard, like pulling teeth.