Galatians 1:11-2:10 The Revelation of the Gospel

For I would have you know, brethren, that the gospel which was preached by me is not according to man. For I neither received it from man, nor was I taught it, but I received it through a revelation of Jesus Christ...But when God, who had set me apart even from my mother's womb and called me through His grace, was pleased to reveal His Son in me so that I might preach Him among the Gentiles, I did not immediately consult with flesh and blood, nor did I go up to Jerusalem to those who were apostles before me; but I went away to Arabia, and returned once more to Damascus.  Then three years later I went up to Jerusalem to become acquainted with Cephas, and stayed with him fifteen days. But I did not see any other of the apostles except James, the Lord's brother...Then after an interval of fourteen years I went up again to Jerusalem with Barnabas, taking Titus along also...But from those who were of high reputation (what they were makes no difference to me; God shows no partiality)-well, those who were of reputation contributed nothing to me.

We can read about the conversion of the apostle Paul in Acts 9. He was on his way to Damascus to arrest and imprison Christians, when a bright light shone around him. He heard a voice say, "Saul, Saul, why are you persecuting Me?"  And he said, "Who are You, Lord?" And He said,  "I am Jesus whom you are persecuting. [Acts 9:4-5]. Blinded by the encounter, he was led into Damascus, where he waited three days before God sent Ananias to pray for him and heal his blindness. "and immediately he began to proclaim Jesus in the synagogues, saying, “He is the Son of God.”" [Acts 9:20 NASB]

We are told in Galatians 1:16-17, "I did not immediately consult with flesh and blood, nor did I go up to Jerusalem to those who were apostles before me; but I went away to Arabia, and returned once more to Damascus."

This isn't a contradiction. The word "immediately" is relative. It can mean "this very instant" or "in a relatively short amount of time".

Although it is not related in the book of Acts, it would appear that after his conversion, Paul initially went into the desert. By mentioning it in this context, he is implying that it was during this time that he  received the the Gospel through "a revelation of Jesus Christ".

Paul clearly states in Galatians 1:11-12 that he did not learn the Gospel from any man, but was taught directly by Jesus Himself in a vision. The Gospel that Paul preaches is the Gospel according to Jesus.

We are not told how long he stayed in the wilderness, but I don't think it was very long, because he returned to Damascus and began preaching the Gospel of Christ. It was quick enough that Luke described it in the book of Acts as "immediate".

He stayed in Damascus and preached for three years before going to Jerusalem (Acts 9:26). The revelation of the Gospel that Paul received was complete. The apostles in Jerusalem - those who walked with Jesus - couldn't add anything to his message.

This is the Gospel that Paul is defending against false teachers.

As we read Paul's defense of the Gospel, let's keep in mind that what he teaches is not just one person's opinion. It is the truth that Jesus communicated directly to Paul.