You've already asked her out, so it won't be as tough the next time.
The best piece of advice I can offer is two-fold:
A) Don't focus solely on her. It can come across to her as a little creepy, plus it limits your possibilities of meeting new girls that you might like.
B) Don't make a big deal about it. Keep things casual and easy. Keep chatting with her, get comfortable with yourself. Use your acting skills if you must.
Remember that you are young and everything is a learning experience. Just keep your head up through it all. Confidence in yourself is the key.
Good luck.
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