Oh boy I hope I just don't post another generic answer to this question.
First of all, I understand the stress and it happens to students throughout their academic journey. To manage stress you will have to determine the aspects that you're stressing about ( not getting the grades you want etc ) and how exactly is not getting what you want affect your short or long term goals.
It's been a decade since I was in your position and there's been numerous times after it that I have felt stress about education. I have failed, I thought I wasted my life and everything but there's something I have realized along the way that's sort of helped me.
In the long run it doesn't matter what your scores are, even if you fail. They will affect you in the short term and you probably would have to work harder as a result but if you're committed and determined, life finds a way for you.
I'd be happy to talk more if you want me to.