Hmm prude eh.
Well my advice is to chill and watch the movie, then sometime during it try and hold her hand, if she isnt into it stop then try later if she is wait a bit longer and try snuggling up to her and being really close, again if she isnt ready back off, if she is wait a bit longer then try run your fingers through her hair, if she isnt into it back off and try later if she is then wait a bit longer then go in for the kiss, then blah blah blah u know how it goes.
idk depending on the chick the movie you seeing and the atmosphere it may not go that far or farther, but since u said she kinda a prude who knows. Remember no one is pressuring you so if the vibe isnt right then forget about making a move because if you feel weird and uncomfortable it may be a crash and burn for ya.
My best advice is dont worry about it so much, she will feel the tension that you give off, just relax and have fun.