Huh, is your school qualified for International Science Fair (ISEF)? Because for that you need a high quality project and lots of forms to fill out. Anyways I went to that last year, it was awesome! And I've been doing science fairs for a long time.
First you should go to www.sciencebuddies.com It's a great site, I'm sure it will help you.
Now you need a topic of interest. You don't need to come up with something too specific but go beying generality. It may come from reading an article or hearing NPR or watching TV, but you should tune up on science and see if anything jumps out at you and you really want to explore it.
Consider how much time you have and how much effort you are willing to put in. This may change as you change your topic (if you find something exciting you'll put in more effort).
Do you like building things, or designing things? Engineering is for you, my friend. You build something, test it, and then redesign it to fit the appropriate result. Anything from robots to biological motors.
Anyways just message me (on my profile) if you need more help. I'd be happy to.