OMG I understand you SO MUCH : I am doing a Spart Race Sprint (which looks a lot alike the Warrior Dash) in exactly 9 days and I am already nervous/terrified.
I'd say that I get the ''omg what have I doooone'' feeling, wanting to back out, until I stand at the starting line and they are about to launch the thing. In the end it's the people around me that get me excited, but it happens at the very last moment.
Like you, I've done other races before but this one is making me feel SO NERVOUS. I'm not muscular and not strong AT ALL, I'm afraid I'll have to do tons of burpees if I can't go through the obstacles...
I can't wait to hear about your race though, I'm sure you'll KILL THIS THING (and maybe that will help soothing out my anxiety

)
GOOD LUCK! Have fun!!!