Present to your parents. To your pets. To your friends. To pictures of friend on your computer. Say it over and over and over until you're sick of it, like hearing a song too many times. Once before public speaking I stood up in my room and talked to my stuffed toys. I was 16 :P . Teddy and Dolly won't judge.
On the day of, think positive thoughts. You'll probably be squirming in your seat, but just remember, your topic is really cool. A lot of people don't know about whorls and personality! You get to teach them something they don't know. They're going to be interested, and leave with some knew knowledge that you shared with them. While you're waiting for your turn, sit tall and confident in your chair. Right before you go on stage, take a deep, slow breath, and smile. There is actually psychology behind smiling, and making yourself "bigger" to stimulate confidence.
When you're up there, if you're being judged, take turns talking directly to the judges. They'll probably be looking at you, and will be interested in what you say. Talk to them! If not, get a friend or parent who is there to keep eye contact with you, so you have something to focus on and not get distracted. If all else fails, look at different points around the back of the room, right over peoples' heads. It makes it look like you're talking and connecting to people around the room, when really you've forgotten they're all there and you're just reciting your "song".
You'll be great :) The more you do it, the easier it is, and it's never easy to start with!