How to perform under pressure

I am a relatively new competitive mathematician and love the style of questions, however come exam day and time flies right by, my mind feels stuck and nothing feels fun. I feel I put a lot of pressure on myself to do well so to progress further, but I topple under pressure. Any tips from experienced competitors? The main points of stress include: “if I don’t do well here, I’ve lost my chance forever” or “I have to prove to everyone I really am amazing at this”. I love the subject and the discipline, but I really need help for exam day.