How long ago did you see her? Have you texted her since? A lot of girls I know get super paranoid about texting activity or lack thereof. It doesn't help that most guys signal that they are no longer interested by never speaking to us again, so sometimes not hearing from a guy we've gone out with after a day or two can make us start to think this is what he's doing. I am apparently very liberal when it comes to how long I will tolerate waiting to hear back from a guy; I've recently made many more female friends than I used to have, and they freak out and even get angry if a guy doesn't text them back within a few hours or so.
Oh, and that's the thing you need to be aware of: First it's "I guess he's busy right now," then it's "Omg he's ignoring my text he must think I'm a loser, boo hoo he doesn't like me," then it's "HOW DARE THAT ASSHOLE IGNORE ME LIKE THIS. FUCK HIM FOR NOT LIKING ME, I HOPE HE ROTS IN HELL." Then sometime after that is probably when you realize you have a text on your phone that you haven't opened yet.
The best thing to do would be to text a girl the day after you've gone out with her and say, "Hey, I had a lot of fun last night! Are you doing anything next weekend?" If it's already been a few days, don't worry yet and just replace "last night" with "the other day" or whatever.
Or, if there's anything you two talked about on your date that would make sense to follow up on, like talking about a funny YouTube video or commercial she hasn't seen, or an article you've read that she hadn't, or a movie that she hasn't heard about yet, or a band she's not familiar with, link her to whatever it was you were trying to describe to her. Don't send a novel of text with it, just "this is that ___ I was talking about: [link]"