do I have to go back to work to file a workers comp claim in california

if you were hurt at work, you should have already filed a claim with your employer. This would get you medical treatment as well as temporary disability compensation why you are off work, and until you can go back to work.   I don't understand very well from your question as to whether you have filed a claim already, or why you are off work. However, you must immediately file a claim for your injury with your employer, and seek medical treatment for your injury.