Im, 13 and I need to calm my nerves! But how?

Okay I am 13 years old and I freak out about everything. I have anxiety and went to a councellor every week for a long time! I am starting to freak out about everything now, tests, quizzes, off-season, etc. The worst is probably sports, I am really good at almost everything but I just freak out. Athletics is at the end of the day, so i am never in a good mood because I'm always so nervous and stuff! How can I help this???