Nah, there's plenty of stuff in the Bible he probably didn't say, but there's also stuff in the Bible we're pretty sure he did say. You have to remember that even in the 50-100 years between when Jesus died and when the gospels were written the "Christians" underwent massive change. You can see people insert more and more material as they get further and further from his death.

Now, I suppose it depends on what you consider massive, but like, Jesus never claimed to be God or the son of God or anything like that. He considered himself to be a prophet warning people about the end of the world where God would judge people for their deeds. This was supposed to happen within his lifetime. There's lots of advice he gives that makes a lot more sense in that context.

Compare that with the stuff we think is later additions to "his" message, and you start to see things that make more sense if maybe the world isn't going to end in the next few years afterall... They also added a lot of stuff that only makes sense if Jesus is divine, which is not something he ever claimed to be. But you can see the divinity crank up the further from his death we get.

I agree that is one of the more common things to debate, probably more common than what he did say. But that's also only true as long as you confine yourself to the Bible as it exists today. When you look into the history, archeological record, and textual criticism though, things get much more complicated as quite a few more groups wrote about what Jesus was purported to teach than the Catholic and Protestant churches would like you to believe.

Robert Price's, "Pre-Nicene New Testament" is a good introduction to just how diverse and radically different early Christianity was. Bart Erhman is another great author who clearly cares more about what's true, than what fits a churches dogma.