Sometimes relocating the scope a half inch or so forward or rearward in the rings will solve a problem like that. Also, cranking the rings down too tight can cause a problem. Taking it off and carefully remounting it may do the trick.
I always center the elevation and windage adjustments before mounting a scope. If it's a gun with a removable breech plug, I mount the scope with the rings very loose, then position the scope and tighten the rings while checking the view through the bore to get it as close to center as I can before using the scope's adjustments.