How do I stop my nerves from ruining my performance?

Your nerves undo you when it counts, and it is maddening, because you know you can do the thing, right up until the moment arrives and your body betrays you. First, know this is not a character flaw or a sign you do not belong. It is one of the most common struggles there is, and it is trainable. Here is the key that changes things. The racing heart, the tight chest, the jitters, those are not proof you are about to fail. They are just energy, your body getting ready. The problem is not the nerves, it is the story you tell about them: this means I will choke. Change the story to this means I am ready, and the same feeling starts working for you instead of against you. So practice one thing before your next competition: slow, long exhales, breathing out for longer than you breathe in. It tells your body it is safe and settles the panic enough to let your skill through. You do not need to feel calm to perform. You need to stop treating the nerves as the enemy. They are just fuel you have not learned to steer yet.