Did I do anything wrong?

Ok I'm thirteen and there is tis girl in my class who I fancy and i asked on here and everyone agreed (she dumped her boyfriend and the started flirting wih me and spending as muchtime with me as possible and staring at me but then she went out with her ex again and stoped flirting with alot(she now nowhere near flirts as much) so did i do something wrong(i was gunna ask her out then this happened) and wht should i do(her and her boyfriend arnt as close as they were)