If your Dr. prescribed you to take them as needed, then only you can be the judge of how often you should take them.
I currently have a prescription for Klonopin (1mg) to be taken twice a day every 12 hours. However, Klonopin has a half-life of 18-24 hours, so in theory one pill a day should be enough to keep your anxiety at bay.
My anxiety is pretty acute and persistent, so even at 1mg, I barely feel the effects and still, I try not to take it too often (certainly not twice/day!). I did take it as prescribed at the beginning and found that if I missed a dose I would get rebound anxiety and get a strange electric shock feeling.
Everybody is different, but the less you learn to rely on the drug to ease your anxiety, the better (in my opinion, anyway).
Best of Luck,