I always get pre-race jitters (and pre-race...um...intestinal issues- sorry TMI) , but like RNRGirl said- once the gun goes off it's down to business and off I go.
You'll have an amazing time!!! Just be sure to enjoy the experience. Look around you, take it all in. You never get that first one back, so don't let anxiety take away from the exciting atmosphere of the race. You're well prepared and you'll have a great race!
Know we're all here cheering you on!!!!!

Good luck!!!!!