Once you have done what skot said, above, swap your mounts over, try front to the back, if to no avail, turn mounts so the dovetail tightening screws are on the other side.
If none of this works its either, barrel is out of alighnment from the action, scope grooves are not true, or the scope is broke. sometimes scopes internals stick, and re-centreing like skot suggested can work.
good luck.
atb phil
some times its the mounts that are the problem, which is why i suggested turning them.