gotta ask this girl out tomorrow

i am not really that popular.. i am a junior in high school and i am just friendly with everyone in my school weather they are popular or losers. this year (junior year) i met this girl who was kinda a bitch to me the first few months of the school year.. i never thought twice about her, but over the last few months i've been really chill w/ her.. we talk everyday during science, but last week we had our seats changed and she lookd really upset.. she flirts w/ me and we have good conversations.. however, all of this has been deteriorating over the last 2 weeks. since we switched seats, i don't sit next to her in any classes. it's been real hard to talk to her the way we used to talk, but we still talk sometimes.. however, she seems less interested than she used to be. i just kinda get that vibe from her. anyways, i have tried to ask her out the past 3 days but i pussied out.. today i was about to do it on the way to a class, but instead of going to another room further away, we went to the library. I have one more day until spring break, and can't go into the break with this hanging over my head. Everyday i try to ask her out and don't, i seem to like her more. i wanna ask her out, and then hopefully if the date goes well ask her to prom


i was thinking of saying something like "Hey, you wanna catch a movie with me sometime" and if she said yes i'd ask for her number. is there a better way to ask her out or does this seem ok? and also if i can't get her on the way to 2nd period tomorrow, i only have 2 more periods w/ her during the day.. how should i get her away from her friends to ask her during those periods assuming i can't ask her on the way to 2nd.

thanks to anyone who helps.. i really appreciate it.