I have answered by IGCSE French Speaking exam last year, the presentation wasn't a problem for me since memorized it to point where I can repeat just from muscle memory. The questions based on the role play and general questions though is a different story, I didn't get extra time which was bad. However as long as the teacher knows that you stutter he/she will understand. Do the best you can for the presentation and try not to make eye contact and zone out while answering questions, this helped me. I imagined I was alone in my room with no one there. Hope this brings comfort and helps you in some way.