Putting pressure on yourself to talk faster will just make the stuttering worse. Just prep well and do your best and if you fail, go above your teacher to complain. Prove you did your due diligence by having good presentation slides, note cards, research paper to show you actually intent to do a good talk. If you do that and you fail, making the case they are failing you due to something you can't control is easy. Edit: You might also try talk to your teacher if you haven't done so already. Let them know you stutter and cannot talk within a time limit and work something out with them.