i'm pretty sure any romantic relationships you make at your age are doomed to fail from the start but whatever, i'll give you my top notch advice anyways.
if you just straight up confess to her that you're harboring feelings for her, she's going to reject you and you're going to forget up your friendship. an exception to this is if the secret love is mutual, but we can't guarantee that so...
the best way to approach this is to not be a spastic forget-up and just let stuff fall in place. be a great pal and maybe some day she'll go for it. if this never happens, you better tame your loving rooster because it ain't entering her anytime soon.