One thing here man. Let's take this out of the "game" for a second. Look at your texts. You're overreacting to miniature things here. Sure you're trying to be playful, but it's not playful if you repeat your point several times.
Quote:
Me: She has GREAT taste. Wear it when I see you next, only that!
Her: Theres a problem my mother decided to wash it so its at home lol
Me: Woah you definitely owe me on this one. tsk tsk you're slacking!
Her: I was in a hurry, going home again on sat il get it then.
Me: You best do, I'll ttyl sexy.
Her: I'll make it up to you.
Here you're making the shirt thing a bigger deal than it is. I'm guessing it's not really THAT big of a deal to you is it? Or is this shirt something your dead great grandmother gave to you as a last gift? If not then, fuck it who cares!
I see what you're trying to do, act as if you are in the power position and not take her shit. Even with your first text of "How's my 2nd favourite student doing, you best be looking after my shirt!" But she wasn't giving you shit in the first place. You're making "shit" up by overreacting to little things.
Imagine you would've said:
Her: Theres a problem

my mother decided to wash it so its at home lol
Me: Well it was either that...or topless. I guess that only leaves one option
Or if you want to tease --
Me: You can't be trusted! I'm gonna have to call the shirt police and hunt you down missy!
Here you are playful, but not in an overreactive way, as it's OBVIOUS you're joking. In the first example you're being playful and sexual. These are just examples, there are many other things to say.
It's best to get out of this mindframe of "I have the power and you do things I like or I punish you" and rather get into the "We're a team, let's play and tease each other a bit." Keep the interaction positive, especially through text. Had you not fucked this girl, I'm pretty sure she would have lost interest as you come off a little overreactive over your little shirt and a bit of a bossy guy too with your last text.
Hopefully this was of some insight to you. You're both on the same team. Have fun. Move the conversation forward in a positive way. Every now and then, maybe throw in a harsher tease, and if she reacts negatively, ignore her reaction and move the conversation forward in a positive direction. (I sometimes full on do the team mindset, if she has a bad reaction, I go "Let's fly to Rome and eat straciatella ice-cream. Wait, can you fly?") Something like that. But that's damage control.
Have fun, be playful. Don't be an asshole.