I was afraid too my friend. Each second that passes towards my turn. My heart beat would increase. No matter how much you overthink or underthink. U will stutter. Best thing I can suggest for you, is to email your professor and ask him if you can give a presentation after the class one to one. Just you and your professor. Of course explain your situation. U jus gotta pray ur professor blesses it. If he doesn’t then just think before you go up “in 5 minutes, I will be sat back in this same chair and it will all be over, in one hour, I will be having lunch, in 5 hours, I will be home.” Wing it bro, stuttering is like Russian roulette, sometimes your lucky af and get a sentence out, and sometimes you get fucked and can’t say a single word. And if anyone laughs at you during your presentation. Fuck dem up