2 3/4" slugs generally shoot better in most guns, I would put a red dot or hologram sight scope on top and use it.
Since most shots will be inside 80 yards it really makes no sense to have magnification on a shotgun scope.
Early morning, and late evening shots will be better served with a scope that doesn't have magnification.
Also a red dot or hologram scope will give your faster target acuisition on a moving target.
If your gun continually shoots off no matter how you adjust your scope, your problem MAY be the increments in your scope or the ammunition you are using may not be what your gun likes to eat.
Try some different slugs and see if they improve,if not, I would get rid of the scope you have and replace it, or check to see if the increments in your scope are centered.