There's a verse in Matthew where Jesus says the pharisees of this generation will have no sign but the sign of Jonah. The equivalent passage in Mark 6, which is set at the same time and place, as is clear from the context, says they will have no sign at all.
John says Thomas was not present at the first meeting between the resurrected Jesus and the 1 other apostles. This contradicts other gopsels which say the 11 were present at the first meeting, after Jesus met Cleopas and Simon. The oldest manuscripts of Mark omit Mark 16:10-20, which has details added in later to reconcile Mark with Luke. Some manuscripts of Mark omit the word "twice" from the quote "before the rooster crows twice, you will have denied me three times" in order to force Mark to match up with the later gospels.These are examples contradictions that never bother Christians but atheists seem to bring them up endlessly. It is important to understand what Catholics claim about scripture and what they don't. I know many atheists get much of their information from fundamentalist sources or even from anti-Christian writers. There are a bunch of things being said about the bible that don't hold up to scrutiny. Still we don't need to defend every claim about the bible. As a Catholic I just need to defend the claims the church makes. So what are those?