How do you stop a crush?

im 13 and a girl. school started back this week. i kinda like my home room teacher/ pe teacher. i don't really know him but i know that he is 24. i had volleyball after school and found out he is my coach. tomorrow we have our first P.E lessen and because it's summer we are swimming- which makes me nervous. i know that its silly to like him. how do i get over it quick?