I think there are two halves - the nervous 'did I do the rights thing' and the nervous 'will I make a fool of myself' <img src="/images/graemlins/smile.gif" alt="" />
So if you think to yourself, I've already made this decision, and I made it fully, then you don't need to get nervous about the 'right thing'. Because the decision was already made. Now it's just the celebration of that decision.
If you're nervous about the 'make a fool', think of all the truly disastrous things that have happened at weddings, and people still had fun. Since the chance of all of them happening at your wedding is slim, whatever does happen will be minor <img src="/images/graemlins/smile.gif" alt="" />