I had a similar problem with a Weaver picatinny rail mounted on my Model 10FP. Tried various scopes, all known performers, to no avail. Took the rail off to look for burrs as stangfish pointed out above, and after finding nothing, proceeded to reinstall. That's when I discovered that the mounting holes in the rail were not the beveled, self-centering
type, but had a squared shoulder for the screws to tighten down on. There was enough slop in the holes that when the screws were just slightly loosened, you could wiggle the rail side to side a little bit. I apparently had it cocked to one side when I first mounted it. I shifted it a slight amount in the needed direction, retightened, reinstalled the scope, and found that I was now close to center. I was somewhat worried that this thing would shift under recoil, but I've got probably 300 or so rounds of .308 through it with no shift in POI. Keep in mind too this was a very slight amount of "slop", but it still made a big difference at 100 yds.

BTW, did you say your bedroom is 18 yds. wide? ???