what i do is meditate. now that takes a long time to master completely cuz u need practice and plenty disipline. and since ur competition is coming up u probably wont have time to master it before the competition lol.
so do a simple type of meditation. find a place thats quiet and where u can be at peace. close ur eyes and breathe. just focus on ur breathing by naming those breathes "in" and "out". empty ur mind of outside noises and distractions. then empty ur mind of all thoughts and distractions from the inside. continue breathing and naming ur breathes. as u breathe relax ur muscles slowly, a few at a time.
this should bring u into peace and help u to relax. do this for at least 20 minutes. i recommend at least 30. it should help to calm most of ur anxiety. when i meditate i set a timer on my phone so i dont have to keep interupting myself to look at the time. that way i can totally focus on meditating.

So just before the competition? Or now?

I think that's a very good idea.. What kind of music competition are you doing? I personally play french horn and deep breathing/relaxation exercises are really useful for calming down for competitions. I would google it and try and find some that you think might be useful for you. I have several that I use if you can't find anything good :)

I play in a rock band, lead guitarist. It was a pretty big competiton, it was state-wide, and we ended up coming 3rd. Pretty happy with it!

I'll google the breathing exercises, thankyou.

I would just take some deep breathes and try to calm yourself a little maybe take a walk that's what i have been doing when i have been getting anxiety plus it helps to talk to someone also.

Thankyou for the advice, going for a walk does help me.