I think she is just teasing you... She wants you to try more...

But i wouldnt try more i would DHV myself and keep teasing her... Make her attracted to you and you will know when she will want from you to ask her for the numb

.
I got my own example... I was teasing one girl, she was attracted to me blabla...
I drived her home one night and we were talking about some cd's that night i must borrow her...
So before she went out from the car, she was like "ohh but how will you give me cd's you dont have my number"... She was actually begging me to get her #

... i played it cool i was like "yah, you can write my number"

. I throw the ball to her field so she had to call me instead

... I knew she will call me b/c of the way she wanted to make me to ask her for the #

...
You do the same... Show her HV, make her interested... Dont push for the number kuz its "cool for you like this

"
But if you really wanted the number than you shouldnt ask her... After funny talk and lotz of laugh... Just take your cellphone and tell her "know what, i rly enjoyed our conv. gimme your number... i promise i want call you more than 40 times per day kuz i dont have that much time... but at least i will call you 20 times per day....hope thats enough?" Tease her with joke like that..
It should work kuz u didnt ask, and you made her laugh so she will be easier to give you the #

.