Why am I so anxious over my grades in school?

I totally get you. Also, now that you've set a new standard for yourself that you're proud of, anything less will seem to be a disappointment. Seriously, though, it's good to be concerned about grades enough for you to put reasonable effort into your assignments, but if you begin losing lots of sleep and being perpetually worried and anxious, it's not worth it. I have anxiety, and I've always been in higher-level classes, but I suck at time management. I did so much last year (my junior year), putting all of my effort into nearly every task and doing extracurriculars, that I'm burned out. My schedule is super easy this year, but I feel like I always have so much to do, and I stay up late doing homework that I could've finished hours ago. Don't push too hard, because if you get burned out, it'll be incredibly hard to recover.

You would have hated my Control Systems professor. He made his exams so hard that the highest score was around 55 out of 100. He made them that way on purpose. He graded on a curve of course, but i imagine it would unnerving for somebody like yourself. In his class, you just had to be better than everybody else, but you didn't know what scores they got until the revealing.