Things like that can happen to anyone under stress, don’t feel stupid! Just try your best to distract yourself and use it to motivate yourself for ur next exams if you have any - it seems like you are getting over stressed, make sure you’re taking care of your mental health, your brain won’t perform at its best otherwise. I’m sure you have still done fantastic. I did something similar in my English GCSE and still managed to get an A* - you have probably done better than you’re expecting. Good luck