I'd throw on a couple of layers of duct tape on the down tube and the back of the seat tube, grab some 25 or 28c Gatorskins, maybe throw on another wrap of bar tape. Swap out to your MTB pedal and shoes in case you need to stick a foot down. I ride on gravel a lot and other than flats it's not a huge deal, just be smooth and keep your eyes up the road for pot holes. The race will probably bust up pretty good so it might not be all that bad a first race once things settle out a bit.