Upcoming oral exam - how to manage extreme stress and anxiety?

Upcoming oral exam - how to manage extreme stress and anxiety? I'm a university student who struggles with both stuttering and generalized anxiety disorder. I have my first ever oral exam coming up soon, and honestly, I’m really scared. My professor has reassured me that it won’t be an issue, but I’m still extremely anxious that my speech difficulties will seriously impact my performance—especially since I’ll have to speak continuously for about twenty minutes. I'm also worried that if I need extra time to manage my stutter, I won’t have enough time to fully express my thoughts and earn the points I need. Right now, I’m feeling nauseous, my stomach hurts, my hands are shaking, and my heart keeps racing. I can’t focus on anything else, and it’s making it really hard for me to study properly. Since my stuttering gets much worse when I’m anxious, I’m terrified I’ll freeze completely and won’t be able to say a word—or that I’ll push myself to the point of total burnout. Do you have any advice or suggestions?