Ever checked out Barber's "Excursions"? I played movement four for state UIL, it was pretty bitchin'. Movement one is more fun to play though, I was ironing it out right before I dropped piano before starting college. Also, Gershwin's prelude No. 3's grand finale was the most ridiculous thing I've ever even tried to do. Now, most importantly, screw performance piano! It's too subject to being human. We can't always be well rested, or in the perfect mindset all of the time. I've been there, stumbling, my teacher bringing out the sheet music so I could find my way back to the route memorization technique that I fell into. Learning a musical instrument is good for your brain in ways that we don't fundamentally understand yet. Piano is also the best instrument for learning music theory, but you probably already knew that. Hang in there dude. No use beating yourself up for being human. :)