I don't know if this is any consolation (I didn't see the performance because I don't get KTLA and I didn't know you could watch it online), but just from hearing what people are saying, we already know what to expect from Utada. But what we should keep in mind is that what's "bad" for Utada may still be way beyond what the majority of the American public unfamiliar with Utada was expecting. I mean, most of the time celebrities come out and just lip sync while they pretend they know how to dance. At least no one can accuse Utada of not putting forth the effort.
Plus, for most people, she's a "new" artist. Struggling a bit is, psychologically, actually a little productive. I'm assuming she did pretty well with "Me Muero" and "FYI" because no one has complained, so the fact that her voice was hurting for CBTM (which is a HARD song to sing because of the random, spontaneous changes in pitch), could possibly give people a reason to kind of relate to Utada. Making mistakes makes her seem more human and shows that she's still a person, just like the rest of us. Especially for an artist like Utada, who already has a musical empire in Japan, this is important because it really shows that she isn't sitting on some throne as an example of perfection- which would just make people jealous. To a lot of people, she's like a growing child just making her way into the United States, and a couple of mistakes here and there are not only expected, but really desired by most people. Humanity is important in art.
That being said, it would be a real problem if she botched "Me Muero" and "FYI" too. ^^;

Kisses & Cuddles,
Shuri/Eli