I was the president of a club in my last year of high school, basically presentations every single week haha. After a while, I realised that keeping calm and focused helps a lot. Because when you're nervous about messing up or the amount of people then you'll do worse. Keep focused on what you're going to say, how you're going to say. If you need to, hold something like a Pen in your hand and tap your hand with it whenever you feel like a block is coming. I always keep my hands moving as I speak with my hands, walk around if you need to but not too much. Look behind the class if you need so. Speak with confidence. I'm guessing most people in your class know you have a speech impediment so they won't mind or laugh or anything. And honestly, when it's like this, I feel more comfortable because I'm not trying to hide it. If I mess up, then I know the class will understand. I hope you feel the same because it comes down to accepting it. And if you're still nervous, practice! Speak to yourself exactly like how'll you do it. Pen in hand, hands moving, etc. This is all an example or suggestions. Also, I suggest going first! Volunteer first! The reason why? Once you're done, you'll feel SO relieved! And also, the more students that go up before you, the teacher will most likely change things up in between. For instance, if a student doesn't say their name, the teacher will want everyone from then on to say their name. If you go first, the more lenient you can be with how you present! Good luck buddy!