You have to remember that if it was meant to be then IT WILL HAPPEN!
You're so young. You're in high school! Trust me, you don't know what love is just yet. You are going to meet so many more girls (whether you say you're good-looking or not) throughout your life. There's still college and beyond that.
Go ahead and tell her how you feel. You have nothing to lose. You never know unless you try. If she rejects you, don't be hurt. It's just one of many learning experiences that you will live and learn from. In turn, you'll grow up to be so much more confident.
If she rejects you, don't be sad. There are so many fish in the sea honey. Enough to go around for everyone!