I always feel a little "nervous" when doing something for the first time or for a new client. As long as you know you're fair in your pricing, you're priced right for the job and believe in yourself and your capabilities, you should be fine.
I think butterflies are good at times, means you have a conscience.
Best wishes, now go LAND THAT JOB!!
(And of course we're going to require before and after pictures so don't try using that ole "I forgot the camera" excuse!)
NJ Lawnmasters, Inc.