Try This One
"Hi ! You know what i see you here and i realize if i dont tell you something i will lose my chance to meet you".After that opener you must find some topic with her and talk 5-10 minutes after that say to her this : You know what i must go because i must now go because my friend waiting for me you know what we have got a very good conversation we will finish this conversation later write me your number here and you will give her your phone after she ener the number you save number.And Say I will maybe call you later wait 2 days and call to her

I tested This by myself and everytime work ;]