Just to clarify Blue, BF is entirely correct. Many people taking benzo's regularly overuse them (or abuse them) and they no longer work like they should. I know someone who has blown through both Klonopin and Xanax doing that.

But you are taking Xanax as needed, so that's different. it's okay to take it more than once a day if you are experiencing strong anxiety.
What's important is that you make sure that you follow the directions that your pdoc has given you