First of all, definitely keep the mic. I don't know why, but holding something in your hands, particularly a mic, will help. Trust me on this. Secondly, just practice it. A zillion times. Say it in the shower. Say it on your commute. Say it to yourself before you go to bed. Make it a mantra. If you know you can get through it when you're on your own, you can get through it one more time. And finally, remember that everyone there loves you and is there to celebrate you. If you stutter a little, who cares? I guarantee you nobody will notice or care or remember. That's not what the day is about.