How committed are you to pitching? Do you like it so much that you want to put in the necessary time to one day be one of the top pitchers at your school? If you have pain now, it's very possible that your mechanics are off ... are you willing to seek the advice you need and put in dozens and dozens of hours correcting your mechanics?
If you really want to be a pitcher, you should speak to the coach and explain that your arm is in pain, and would rather not push it for a pitching tryout --- that is a recipe for almost certain injury.
However, if you would be just as happy simply making the team as a position player, you may want to put down another position.
Either way, you may want to speak to your coach or find a good instructor to evaluate your throwing mechanics. Pain in your arm is often due to either doing too much throwing before you're ready, or poor mechanics.