First you need to be congratulated on taking a step to say hi, You have actually gained some points on getting her number. I know that is usually the hardest part for guys when they show interest in a girl. Anyway the fact that she was able to give you her number that is an indication that she may be feeling the same way too, lets just say that the feeling is mutual. Girls like to be approached, they don't want to be seen as the ones making the move. that's why they play hard to get sometimes but if you push a bit you just could end up being the lucky one. here is a tip, if a girl gives you her number she expects you to call her, i don't know if you called on the first day, or you took some days before you did it. since you have been calling her i guess you have your ground and can be able to talk to her freely. why don't you take the first step and ask her out am sure she is looking forward to it, do not waste time otherwise you will loose her trying not to look desperate. A simple date will get things rolling maybe a lunch date or a movie will do, then on the date get to know each other better. do not try to do anything funny just be friends and you can move on from there ALL THE BEST.