I'm so angry/upset about my maths exam!?

well basicaly i knew i done a question wrong,becuase i worked it out and relised i got it wrong and put another answer in my test paper. Urgh,I cannot cope with myself I feel so angry and p*ssed off. What should I do? Now im gunna get a bad grade and move down and not up in my sets. I just blew it and I'm working so well, Urgh I just want to scream I hate myself. Any advice you could give me. Thanks.