If you are to see a girl every day at school or what not, you need to have some serious game if you just want to mess with her and don't want a relationship. Not because of the girl, but because your desires will get the best of you, and before you know it shes your new girlfriend.
Make sure to keep busy during the three day period. I keep a schedule book, so write on the third day "call so and so." Then I completely forget about her. on the third day I see her on my schedule book, and call her.
You want to think about her as little as possible during those three days. If you get to the point where you practically forget about her, then your money.