Was Paul still working with Peter and the twelve apostles when he wrote 2 Corinthians?
No. When Paul wrote 2 Corinthians, he was no longer working hand in glove with Peter and the eleven. He was proclaiming revelation they did not know, which led Judaizers in Jerusalem to accuse him falsely. The context states he was not agreeing with them anymore.
Les explains that Paul did not come with fickle language; his message was prompted by the Holy Spirit and constrained by the love of Christ. In 2 Corinthians he lists privation after privation. In verse 17 he was accused of not bringing the truth because he was not agreeing with the Judaizers in Jerusalem. He was not working hand in glove with Peter and the eleven anymore. He was proclaiming something they really knew nothing of, so he was bombarded with false accusations that should have been reserved for false teachers. Les notes that those with the truth often come under attack instead of the false teachers.