You need to ask girls out earlier into the interaction.
If it's going well 2-5 minutes in, even if you'll be there another 10+ minutes, just tell her "Hey, before I forget, we ought to trade cells so we can link up later for food or drinks or what have you." Then just grab her contact info.
When girls give you lame answers, just tease them a bit.
Like, seriously, "None? Okay, so you get home after class, toss your school bag down, and stare at the wall for a few hours until it's time for dinner. Transcendental meditation? Seriously, how do you spend your time?" grinning and half-laughing the whole time so you know you're teasing her answer, not her.
When you get lame answers, make it a fun thing: "Oh come on. I can't believe you just pick at your toenails five hours a day. You must do SOMETHING. Watch Netflix? Browse animal porn? There's gotta be something!"
Make it fun. You let her feel boring. Don't do that. Joke around a little with her. If she isn't an interesting person (at least superficially), she needs someone who can help make her feel interesting.