Girls, help! I need advice for this girl I like?

It is very hard for me to talk to my crush. We are friends and we tease each other but I struggle with flirting. I always wanna come out and be this really sweet and romantic guy, but we're only in high school so I'm afriad of scaring her away. I end up saying "you look nice" instead of "you are beautiful." Also she's usually really busy and we don't hang out all that much either. I usually only see her in this club that we're in. She also gets pretty stressed out about things and I try to be there for her becaue I like her a lot. She knows I'm interested because I say things like "I wanna take you out sometime" when she mentions how busy she is (she always says something like she'll have to check her schedule). I really want to ask her out to this movie that comes out at the end of the month. But I feel like she isn't really interested since we hardly see each other. Any advice?