Anxiety doesn't mean you are useless. Sometimes it gets the better of us, and that's okay. We can try again next time. I have had panic attacks from fear of heights one day, and then gone rock climbing another day for example. Having the idea to try something new is a step in and of itself. Maybe you can try again sometime if you would like to. I don't think yoga has to be about succeeding at it or not, it is more about the process in my opinion and getting what you need out of it.