Try to keep these thoughts at bay via mindless activity and humorous banter with other runners. Then the start line, and we're off and running. Suddenly the fear evaporates. We're doing it. Whatever happens, happens.
Physical activity is great for the nerves.
Well, chances are you have. But the one thing I try to keep in mind when it's getting close to a race is a saying that I believe Lady G said. Although I'm not facing a 100 miler there is a 100K a couple of weeks from now. In general I'm starting to feel worse about 1 to 2 weeks before the race. I didn't know they existed.