If a girl asks for your number, you tell her, "Only if you give me yours first"

By giving her your number, you set yourself up to be the one waiting on her. That's a very wimpy situation to be in.

When you see her again tell her "You forgot to give me your number." and get it from her. After a few days, call her and invite her to drinks. If she says yes, proceed with date. If she says no but makes a different offer, proceed with date. If she makes an excuse and doesn't make a different offer, sorry, no bite.