If people expect you to ace everything, because you did so in the past, it tells a lot about them, not about you. Nobody is perfect, nobody performs 100% all the time. So try to get things back to perspective. Your first exam was really good, your second, while not so good, wasn't bad either. You have the capabilities to do well, if you keep working for it you will do well. Will it be perfect, or even as good as people come to expect? Maybe, maybe not. But even if the latter is the case, chances are really high that it will still be good, or at the very least good enough. No need for your self-confidence to go all down the drain because one exam went a little less good than you would have wanted to.
It's a shame you can't do your running like you are use to (I assume you still can't), because that would be great to get your mind free from all those thoughts. Try to find something else that relaxes you, that cleans up your thoughts. After that, carry on working for it again. If the high stress levels come back, read this again, go out and relax again, and get to work again. Rinse and repeat

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I know this is easier said than done. But I hope it helps, if only just a little bit.