Ouch! If you got back up and rode after falling like that, don't sweat the race. Think about how tough you are, get on that bike and ride. And most importantly, HAVE FUN with it. You can do it!

Regarding unclipping: perhaps something was stuck in your pedal or cleat making it hard to unclip? And sometimes it just takes a few rides to get new clips settled in.

Regarding a new helmet: if you are at all in doubt about a fall, get a new one, especially if your current one doesn't fit right. I'm on my second Trek Interval having replaced the old one after a head crash earlier this year. I love the dial in the back that makes it easy to adjust the fit before or during a ride. Sometimes I still have to readjust the chin strap after sweating a bit, but I think you'll find that will most straps. I have the women's model as I like the color choices better and they have both xs/s and s/m sizes. The Trek web site lists it at $69.99, but my LBS sold it for $49.99. They also have a 1-year crash warranty. So if you crash and hit your head within the first year of ownership, they will replace the helmet.

Good luck with your race!