I am just repeating the literal words of the bible.
When Paul was preaching to the Gentiles he had all mannor of physical suffering (may had to do with his prison time). What he is talking about here is not a deficiency of the Cross but his own personal physical sufferings that he suffered as he preached the Good News. He preached that Christ suffered on the Cross to atone for sin. Paul is preaching he accepts his physical ailments while preaching on behalf of Christ. So you are saying the Paul is wrong and the Bible contains error? Because the literal words say different. Oh wait I see you are one of those that when Jesus says "This is my Body", "This is my blood" think he is lying. well he we think that the words in the Bible are the truth.
When you read scripture it will help you if you have some historical perspective.
No, I do not believe Jesus lies, even the claim is ridiculous.