Well at this point its all mental. You're not gonna improve much of anything but your attitude.
Get good nights sleep. Try deep breathing and meditation, even a couple minutes before sleep, and before tryouts. Clear your head.
Some would suggest, if you're of the proper mindset, prayer... Even something simple like "(God or universe or earth mother or whatever you believe) please help me, your will be done, thanks" just does the trick for some people to let go of trying to control or worry about everything and let themselves actually be the best they can be.
I agree with the above reply. Belief in your will, belief in your faith, belief in your god, if any. And you will give your more then 100%. At the sametime do not be afraid to fail as long as you are giving your best. Beyond your best. IF you fail this will only make you bigger better stronger and faster for the next time. Quote." I have missed almost 9000 shots in my career, i have lost almost 300 games on 26 occasions, i have been trusted to take the game winning shot, and missed....i have failed over and over again in my life, and thats why i succeed." (One of the greatest basketball players ever...Michael Jordan) Good Luck..you will be great.....
Well if I were you I would at least do 20 regular sit-ups and 20 lotus crunches and do these workouts every Monday,Wednesday, and Saturday. And you will see results and I am serious because I got abs and it really works your core. And do some muscle workouts to like right concentrated biceps curl and left concentrated biceps curl. And any other muscle workouts you want to do.