Gal 2:11 But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed.
Gal 2:12 For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
Gal 2:13 And the other Jews dissembled likewise with him; insomuch that Barnabas also was carried away with their dissimulation.
Gal 2:14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?
Peters actions in the Galatians passage reflect his error in respecting the people who he thought were from James who was the leader of the church in Jerusalem. As you can see the word sin is not used in that passage. Paul accused him of saying one thing and doing another which was true - but there was no intent to deceive.