My first suggestion would be to stop feeling guilty when you make a mistake. Yes, you'd like to make as few as possible, but you're trying as hard as you can under the circumstances, and you're human, and no human is perfect. We all make mistakes sometimes, even the best of us, and schedules often slip as a result. So, relax a little. This doesn't mean you stop caring; it doesn't mean you stop trying to learn from your mistakes; it just means you don't feel guilty about them.

Secondly, try to get as much rest and exercise as you can. This is very important.

I do agree that you should complete your promised deliverable; it's the right thing to do. But after it's done, do see if you can get two or three weeks off, at the very least. You know you're starting to burn out, and it's not in your employer's interest to burn you out completely. (Point that out to them if necessary.) If your finances allow for it, you could perhaps take an unpaid leave of absence.