Many times people will say that they are nervous when they really mean they are excited. There is a vast difference.
Excitement is an energy you can use to make a performance sparkle. That isn't to say that there aren't people who get nervous. While searching out other choir blogs I came across a great article on how to deal with those nerves that can stop some people from even attempting something new. Check out 5 Ways to Deal with Nerves. I couldn't say it any better.
In any situation, as Elena suggests above, when the butterflies start flying in formation the nerves become excitement which you can then share with your audience. Smile, and sally forth.