I'm thinking you're a perfectionist...yes? Perfectionists tend to set goals and then go "balls to the wall" to achieve them. When the time comes for the big challenge they get scared they won't do great.
I've never raced before, but if I may be so bold as to give advice remember you're racing against the clock. Don't worry about all those other people there. They're just there to give you motivation to pass them...it's just you...you and your bike.
Tulip gave good advice...stay away from the crap food. Believe me I love crap food! And occasionally I take a break from healthy eating and binge...and then I feel sluggish...just miserable.
Take a little break, get off the bike, eat healthy and be good to yourself, and give yourself a pep talk. You've done a lot of hard work girl!
Look Back...Look Ahead...Live Now!
2010 Cannondale Synapse 5 Carbon-fiber road w/ a dbl
2007 Trek 7.3 hybrid