How do i break up with someone , or fix things?

First things first this is first relationship.I`m gonna be in a quinceanera and my gf is in it , well that`s how i met her. I recently have lost all interest in having a girlfriend because of the following reason. My gf apparently seems to like my friends more than me cause she ignores me a lot. and i dont know whether to break up before or after the quince cause id have to see her and shes my partner (like 2 weeks til the party. I don`t really know what to do , ive already had a talk with her and it only lasted one day before it continued. One day at quince practice she was telling everyone , one by one about something and only one left is me , so my friend tells her to tell me and her response is that i had already heard what she had said. She hardly pays attention to me and everytime i go to practice and see her (btw i use to see her even when there wasnt practice) instead of feeling happy i feel terrible and i don`t think thats what havig a gf is all about.