I got scratch by a stray cat 3 weeks ago. the scratch is about 3inches long but not deep.. should a worry about rabies? do i need to get antirabies vaccine?

Hard to say: Rabies is a regional issue.Your local health department would have data on if rabies is active in your area as well as a supply of vaccine if appropriate. Feral cats would be an unusual but possible problem but again local health officials have that data. Three weeks is getting a bit late to start looking into this. Cat scratch fever & tetanus are other germs to consider.