Even if you don't feel confident, act the part. Pretty soon you will find that you really do feel confident.
If anyone teases or puts you down because of your hair, stay cool, don't get defensive, and just say you prefer your hair curly.
I know this isn't for everyone, but personally I'm okay making light jokes about my hair when I'm around certain friends. It shows them I'm not sensitive and accept my hair the way it is. Some of the people who make fun of me also let me know they love my hair when being more serious.
And remember, high school will be over soon enough.