Most Helpful Girl
If she is uninterested than that can't really change. She might not be physically attracted to you and that's hard to change. Sounds like she's not the one ):
Most Helpful Guy
It sounds like you put yourself in the friendzone from day one and thought she'd just let you out once you worked up the courage to ask her out.
You'd best think a long time about whether you are capable of being just friends with this girl. If you're going to remain friends then you need to remove her forever from your mind as being a potential mate. That means you NEVER ask her about being romantically involved again and you also never ask her why she said no; and you must never hold it against her that she turned you down. That has no room in a friendship.
If you can't do all of those things then you need to tell her your interest in her is romantic and you can't see her as just a friend. Wish her luck. Tell her you'd love to hear from her if she ever changes her mind. Then tell her goodbye and never contact her again.
This may sound harsh, but you are the one who changed the dynamic of your relationship, and if you can't honor her wish for your relationship to stay platonic, then you owe it to her (and to yourself) to explain that and to end it.
What you cannot do is agree to stay her friend while harboring some secret agenda to make her love you in the future. You will only end up hurt and humiliated later on and you will have deserved it.