Well, for starters, good luck with your tryout.
It's kind of difficult to give you tips on your swing when nobody on this board has seen it (to look for mechanical errors, adjustments, etc.)
If you've been struggling lately and you have been hitting good before that it is very possible that it is something going on between the ears...
I have gone through a very similar experience, i was the middle of the lineup guy that cleaned up after the clean up guy..whatever he didnt drive in..
One thing that can help is just go over your swing in your mind...stick to the basics, it gives you less chances to screw up..baseball is, after all, a negative game, failure and how you deal with it..
Make sure that you have lots of confidence in yourself..and if you cant actually have it, act like it..I know one thing that went on with me was when i was hitting good before the slump was that no matter what the count was, i was confident that i could take what the pitcher threw me and that i could hit it hard somewhere..when i got into the slump i lost that confidence and i started trying to be a contact hitter..
something to chew on