Had same problem with M305 using A.R.M.S M21 mount.
Got rid of it, got a Sadlack Airborne, now it's perfect.
But if your mount is solid, you could get adjustable rings to compensate. Try to get the scope physically as close as center as possible. If you must use large number of clicks to get it centered, something is wrong with the mounting to start with.
Nic