As a lot of people are saying here, you're probably too far behind at this point to reasonably pull it out of your ass at the last minute.

I might study what you can of what you haven't gotten to yet. Start with high level overviews before you get deep into the details of any one section. This is probably futile if you're less than halfway through the material though.

Whatever you do, set a hard cutoff time to just stop, stop worrying, accept whatever is about to happen, and go the fuck to sleep. You aren't getting through it all in one day. Better to get a good nights rest so you can demonstrate well the bits you do know, and brace for the impact.

Moving forward, learn from this panic and worry.

I've been where you are, trying to crunch last minute to pass a class or a test, more times than I can count. My original university put me on academic probation: "We don't want any more of your money unless you're going to pass your classes"

A US university saying no to money. Fuck.

In the future you either need to keep up with the work, or notice that you aren't/can't/don't feel like it and pull the ejector seat handle earlier. Stop trusting the voice that tells you that you'll be able to crunch it at the last moment. You need to be brutally honest with yourself about your own limits, at least internally.

Professors will often work with you if you come to their office hours and talk to them early, but every single one knows when you're coming in last minute as fire insurance. You can also drop a course before you get too far into it.

3 feet before the cliff is too late to worry about pumping the brakes. But if you can get back up after then you can do better next time.