There are some people who get really nervous before making a presentation. Don’t worry, this is quite common. To help get over those nerves you could try some breathing exercise, which should relax you and put yourself in a better frame of mind. Here is one that I have tried.
Place your hands on your ribs and take a deep breath and count aloud on that one breath. Repeat several times, trying to increase the number you are able to count without straining and extend your voice to the far corners of the room