My only advice is that you should not overthink it too much. It's basically another committee meeting with more intrigue surrounding it. If your other committee meetings have been going well and you've been getting through them, then you can guess what your defense will be like.
The defense is more of a ceremonial activity anyway. By now, you should pretty much know now that you're going to pass and there is really nothing that you can do in the next 3 weeks to make a difference. Show up prepared, answer all the questions to the best of your ability, and that's it.
Rest well knowing that people who are not going to finish their PhD never make it this far. I know, people sometimes "fail" their defense, but all this means is that the committee asks you to make some revisions, maybe do a few more experiments, blah blah blah, same old story...