Senior year of high school, running in the regional race, tried to make a move around a pack by going just slightly off of the trail and through a bit of brush. This was about 1.5 miles into the 5k race. It didn't look that bad, but a huge f***ing weed with burrs all over it was waiting directly in the path that my groin would take. Needless to say, I wish I had worn spandex under my shorts that day like many high schoolers do. Don't even rembember what I ran, but it was definitely slow, as I finished well behind my other six teammates. It was all good in well though, as the rest of the guys had good enough days to pull out the victory.
I know my story doesn't quite apply to what you're going through, but I'll just say don't worry about it too much at this point. Maybe if you're still running a lot slower than you'd like after a couple more races, but a lot of shit can happen. You could be tired from training, even if you don't really feel like it, you could've just been off on that particular day (look at Geb in London, it obviously happens to the best too), or the course could've been a bad match for your racing style. If it's just one race, I would've been pissed for a little while that day, but from then on out I'd just get back to training and forget about it.