Don't be afraid to do a cx race on your MTB! I've been beaten by people on their mountain bikes in cross races... Keep your clipless pedals on for the race - you don't really want to use platforms. The biggest challenge will be in carrying the bike, but if it is reasonably light, you won't have a problem.

Have FUN! Cross is supposed to be about fun, and it doesn't matter what you race on!

SheFly