I need help with a girl i like?

Hi im really need help. I have a problem talking with girls straight on i mean its pathetic. If i with a group of girls and friends i can say jokes non stop that will make the girls not stop laughing but if im one on one with them im dumbfounded.So anyway theres this girl in my phys ed class which is about 200 kids. Im a junior and i think she is a freshman or sophmore. i've thought shes really cute for a while now, and theres only 3 days of school left. i dont know her name, or anything about her. i've made her laugh a couple of times though when we were talking with a group of friends. and lately shes been stairing at me alot and smiling then looking away quickly. i dont know if im seeing things or tricking myself, but i want to say something to her tomorrow. is something like "hi, whas your name?" then respond with mine. and then say." i know this is kind of late to tell you but i think your really pretty, and i was wondering if i can have your phone number?" is that any good? and i feel like a stalker cause shes caufght me looking at her a couple times and i make it soo obvious. can anyone help a guy or a girl?