Is there anyway I can get a supervised visitation order changed and if so what forms do I need to file? Should I file contempt or order to show cause

I am in California and here is my situation. I am the NCP with a stay away order from my sons mother. That is why the court ordered supervised visits through a family service center in Nov 2010. The center allows me visitation once a week for 2 hours. Since Dec 2010 I have only visited my son 12 times out of 36 because his mother keeps canceling. When I show up at the center they tell me she canceled again. I have been documenting everything. I am missing out on my sons life and want more time with my son who is 2-1/2 yr old. I feel she is interfering with my parental rights and need to know if there is anything I can do.