Learn from my mistake here. If you keep up what your doing, just chatting her up and "making her laugh" too long. All your ever gonna be is Pen Pals. That's it. All your really gonna do is be a entertainer for them and nothing else.
Think of abundance mentality. As if your talking to 10 other girls right now. You would not give a fuck and just ask her out right? Do exactly that. Right now, all your really doing is being afraid of rejection.
To ask her out. Invite her to an event like a friends birthday, join you for a hobby you enjoy and teach her that, if nothing else is going on, just set up a date at a fun spot, like bowling.
To increase your chances her getting to come out, keep the invite flirty, and don't ask. Keep the assumptive frame that she is coming out if she replies with a "maybe" or "she will try."
Example:
You: My good friends birthday this Saturday. Secret mission is the get the bday boy drunk by midnight. Roll through. (keeping the invite flirty)
Her: I got work in morning so If I am not to tired I will

(she says maybe)
You: Sweet, is at Xtown and it start 10 sharp. We will make sure he doesn't remember his bday

(assuming she is coming. Do not give her all the details yet. I purposely left out the exact address)
Her: Blah blah blah (whatever she says, don't reply back. If she doesn't reply, your can still get her to come out)
Next day few hours before the event.
You: Here is the address XXXXXXXXX. We got so much alcohol! Making a pit stop and picking up 2 bottle 7up or Sprite would be so awesome

(Your still assuming she is comming, but your making her jump through hoops. In this case, is 2 bottle of 7 up which cost less then 3 $. No other guys do that)
This is pretty much a blueprint. I don't remember the exact texting word for word but I had a flaky girl show up doing this for my friends bday. Same concept for other things, even like going bar hopping. Is not gonna always work, but it should increase your odds. Don't be a retard and adapt to what your gonna do with her. For example, if your taking a girl bowling, you would not ask her to bring bottle of 7 up.