1. You are more than your grade.
I know this is very hard to accept, because these are the grades that actually matter. Grades and school are extremely important, but it's not healthy to shrink your entire being to one grade in one class. You are so much more than that grade.
2. You are loved.
It's important to remember that you have people in your life that love you and will do anything to help you. While they can't take a test or finish a project for you, they can just be there to listen to you rant, and sometimes that's all you need.
3. Don't sweat the small stuff.
This is also really hard to accept, especially when there's so much weight given to the last assignments of the semester in college. It might seem like every problem you're faced with right now is impossible. Just take a step back and breathe.
4. Take a break.
Taking a break from what you're doing and coming back to it later with a fresh set of eyes will provide so much clarity. You'll be able to find a solution that was sitting right there all along. This will help so much because you'll be much more calm and ready to tackle the problem or assignment.
5. Everything will be worth it, soon.
Remember that while you're extremely stressed out right now and you might not have everything figured out, everything will be worth it. In a few years, all of your angst and stress will be a distant memory, but a constant reminder of what you had to do to get to where you are.
6. Even if it doesn't turn out the way you wanted, there is always a way.
If you don't get a good final grade in the class, there are ways to fix that. If you don't get accepted to your major, you were meant to be somewhere else; you just have to find it. If you get set back a semester or two, that's perfectly fine, because it's your degree and you work for it at your own pace. It's not the smart people that are successful; it's the persistent ones.