I don't post much here, but I read a lot. I also do a lot of competitive shooting (as well as teach it). The same problem creeps up there too. The parallels are really interesting. Anyway....
It's all in your head.
To perform at your peak level, you have to be mentally prepared for it. If you go in with the attitude that you have (slow, crap hill, etc.), then you won't be able to perform. If you go in with a positive attitude (I can't wait to ride!), then you'll do much better.