Stupid question, obviously you are. Alright so the line between carelessness and no self respect is basically the difference between you genuinely not caring what she thinks and you trying to comply to whatever she thinks. Its the way you would frame your response to her getting upset at you making fun of her. She retaliates and says "But you like twilight more than me!" Say something back like "Fuck yeah I do, I'm basically Edward Cullen, still doesn't excuse the fact that you like twilight

" So you are conceding that you do indeed like twilight but you're still keeping the focus on her. You're keeping it fun. The wrong response would be "Yeah I'm sorry I was making fun of you, Twilight is awesome." That shows that you are just complying with whatever she wants. Bad.
The way you responded was meh. It was somewhere in the middle of the examples I gave. How that comes off is that you care what she thinks (because you probably do) but you're trying really hard not to care. Also it's really hard to convey the tone that you want through text. So, by saying "Busted, Let's keep that between us." with no emoticons or indications for what you were going for, it could come off as you being insecure about you liking twilight. Always make sure the tone of your texting is really easy to get or else you'll get burned and have to explain what you meant and it's shit.
If you want to keep going on this twilight thread (and bro c'mon, twilight? haha) then yeah it would be cool to amp up your own fanaticism to legendary levels. Exaggerate the hell out of it. But please for the love of god make it funny and understandable. Also if you already have comfort with this girl switch to sex talk as soon as possible. That's really all texting is good for. If you want to talk about twilight, talk about twilight in person over coffee.