Why do I have inflammed scar from catscratch?

Possibly infection. Bartonella henselae is the bacteria that causes car scratch fever. This is more likely a local infection by a simple staph or an inflammatory response. Try washing the area well and covering it with neosporin.
Allergy or infection. Could be allergic reaction or infection . Infectious agents from cats include toxoplasmosis. See your doctor to have it checked out. If there is a red streak moving up from your scratch area then this would be considered an sign for emergency attention.