Hey mate.
quite the story you got there.
Look, the first thing i do got to say is: great job on telling her. Lots of guys here would disagree, but i believe in having balls to say what is on your mind. Perhaps you should have told her in the face, instead of text, but still.
Then secondly: instead of just telling her that you like her more then just as a friend, tell her what you want. Its not only saying what is on your mind, its also stating and going for what you want!
Now, on your friends, it seems like they are still a bit childish. Making you feel awkward because you said what you said. I know this aint easy on your age, but try to disregard the childish reactions. Always think to yourself:at least i am on my way to change myself. change is evolution amigo. Change is power. you kinda remind of my meself.
As of the girl: from what i can read: she isnt interested in you. its not really friend zoned. You are using pick up terms, but actually its just age. You say this girl is 15? That is also still a girl. its a freaky age, in which popularity is king. Although you told us not to tell you: dont say leave her alone, this is what i am going to do.
Leave her cold and focus on your personal growth. Expand your social circle, widen your horizon. You are really into this DJ thing, then man, go for it! grow in it! Make yourself happy, then start doing some real seduction, or at least, start learning it

.
Start from the start, and you will have guidance here for your questions. dont come with questions of stuff you read but not tried.
Grow and leave her cold. Keep cold contact, never be unfriendly to her, just take your distance, while you grow. Your time will come, have patience.
cheers.