Scratched my 5Dm3 sensor

i'm pretty sure those are not scratches., but smears of dirt residue. sensor corners and edges  are notoriously difficult to clean. i once had an epic, almost psychotic sensor battle with a little sony  slt-a55 sensor myself.  i learned the bulk of my  sensor  cleaning tricks then and am now very relaxed about  this  business with my 5D3.  take the camera for a professional cleaning.  show them your problem and see what they can do.  you will find out it's just dirt.

good luck!