Ok relationship help with a girl?

i am a junior in high school and i want to ask out this girl named Erica and i want to ask her out and next year her boyfriend is leaving our school so they wont see each Other i predict they will break up and we have been friend for a year and she sometimes pes me notes that she loves me and i just rilly dont want to screw it up i have been waiting a year and i do not want to screw this up please help me just any advise is better then what i have now