I was in a similar situation ... twice. So, write the speech of course. Rehearse the crap out of the speech as best as you can. Out loud, whisper, it changes your tones of voice. Maybe present it to someone you live it or some stranger online if possible. But definitely rehearse the speech. Trying to 'wing' a speech as a person with a stutter is asking for problems. But if you treat it like a drama class and you're just reading out your script it might be more favorable. I don't know much about your stutter or you and given the diversity of stuttering and the emotional response each person has, it would be impossible for any of us to get inside your head and feel what you are feeling and your stuttering related anxiety. Good luck and remember it's not the end of the world.