I used to have a job where I had to speak in front of big crowds. It is normal to be a little nervous. #1 know your material- don't make a speech that has to be said exactly like it is written, or when you stumble, you will get flustered. Instead write each topic section on an index card, and the main points about it. The sentences will come.
Try to practice a little in front of friends.
If you will have a friend in the audience- and there is to be a question section afterwards, have him or her have a question you know you can answer- it will make you feel better when some come in that you may not know the answer for.
If all else fails, picture your instructors in their underwear.