No, but you'll feel more confident and the audience will enjoy it more if you do.
The more experience I get, the more I appreciate the chance to rehearse in front of a small group of friendly tellers. (I've never met an unfriendly teller, but was told to reassure newcomers that we're friendly.) The first telling to an audience is always rough. You forget things, or realize your tongue can't get around those words, or the audience is confused, or there's a second meaning you hadn't thought of, or any of a dozen other things.
My other guild includes former presidents of Storytellers of Canada - Conteurs Canada, and workshop leaders from the Storytelling Toronto. These tellers know what they're doing, and they still rehearse their stories in front of a small group of fellow tellers before the first performance.