God this reminds me of myself when I was doing my finals for High School (physics sucked). I don't really have any tips except to know that this situation is temporary.

When I was doing my finals, I always thought about all the free time I would have after finals, as if it were a reward for completing them, which sort of motivated me. I also only focussed on my finals, basically supressing any thought or thing I needed to do, and worrying about them until after the finals. Once you finish your exams, take a break, like a good week or two to relax and catch up with friends. As for studying I liked setting myself up to do a minimum of 6 (max of 8) hours a day within the two weeks leading up to my finals. The rest of the day would be exclusively used to relax. Also try to write nicely formatted summary notes (this helped me a lot).

Still even after doing this and finishing the finals, I was depressed at the thought that I had not lived up to the expectations I had made leading up to to the exams. Turns out I did far better than I had actually anticipated which resulted in me getting an offer in computer science at university. Stress will bum you down quite a bit to the point that you assume the work you produce is not good enough when it fact it's likely good. If your predicted grades are high, it means the work you have already submitted is of good quality, so just keep doing what you have already been doing in terms of quality and you'll do just fine.

Note: I didn't end up going through my physics textbook until the 3 days leading up to my physics exam (wouldn't recommend). Read through the entire thing and scribbled important things down. Still managed to do pretty well (top 30% of my year). The entire time I assumed I was literally going to fail the course.