I always mess up when I try to play something exactly like a famous guitarist plays it. I realised that it wasn't natural for me to try to play like him. I decided to play his licks my way, even if they don't sound has good. I try to put a little of my style into each of them. Maybe I'm just lying to myself but it works for me. It's hard to explain...

Now when I play a lick from Satriani, it doesn't sound exactly like Satriani, it sounds a little like me.

And try to relax!!! I know I get frustrated and mess up even more.