Check all of the mounts as others suggested first.

If its shooting to the same point of aim every time but with bigger groups, you probably have a parallex problem. If you put the gun in a steady rest and move your head a little bit while aiming at a target at 100 yards and the crosshairs move, this is what is called parallex. The parallex correction for your scope might be set at a longer range such as 200 yards, try shooting at a longer range to see if your groups don't tighten up.

Also check to make sure that your barrel isn't fouled up with copper- give it a good cleaning.