You're attitude should be "Nothing is a big deal."
There are many reasons why she might not seem as hot for you and they don't necessarily mean you've blown it.
Now, I'm not qualified to really give in-depth advice from the perspective of a PUA, but I certainly am from the perspective of someone who used to be a major AFC and fucked up COUNTLESS times with girls!!!
Absolutely do not talk to her about why she isn't acting the same way, don't bring it up, don't get upset about it and don't let her know its upset you! If she's not responding to the playful teasing and negging, then maybe cut back on it.
I'm not saying you're the kind of person who would mope, but just in case, DON'T mope around over this because you will completely kill it. I know from experience.
Also, keep your options open and talk to other girls, don't fixate on this. I can remember many evenings spent running through various encounters with girls I liked through my head, over-analyzing and wondering what I said/didn't say and did that went wrong, it's easy to do and very counter-productive.
Focus on being happy, interesting and fun to be around. You don't know everything about her life and can't assume that there aren't underlying issues in her personal life that might be effecting her interactions with EVERYONE and not just you. But also, brace yourself because yeah, you might have fucked up, and if you have just remember that it's no big deal.
