When you left her that day, did you tell her you would text her? When I've read your initial posting again, she told you that she'd let you know and when she had free time. I wonder if that meant she'd text you?
Regardless, I see nothing wrong in dropping her a text, 'Hi there, was just thinking about you and wondering how you are doing. Sorry for not texting sooner but I've been having problems with my phone connection lately'....something along those lines. Let's her know that you are thinking about her and that you are still interested in a next date with her. You may also be able to gauge further and her level of interest and depending upon how she reacts.
Personally I think those rules like waiting 3 days and 3 seconds to call is a load of rubbish. It's just game playing and game playing can end up backfiring in your face.
It doesn't make sense and to play games with people you like - if you like them, let them know and if they like you in the same way...no one is ever left 'second guessing'.
Good luck anyway, let us know how it goes