Kate M.'s answer was spot-on!
We can get nervous for many different reasons. It might be fear of a bad grade, or of being laughed at or judged harshly, or even fear that you will misrepresent a topic very near and dear to your heart.
When you have the choice, it can help if you can choose a topic you are personally very excited about - one that you can talk about or already know well as long as you don't get too emotional to speak clearly.
When you don't have a choice on your topic of presentation, make sure you become knowledgeable enough to speak with confidence. Check out extra books on the source materiel and look up videos online of similar presentations.
All of these aspects can help you stand in front of a crowd of strangers and bring your best.
Best of luck on your projects! :)