I can't imagine that my ideas could be the only problems there could be many I can't think of off the top of my head. Some people have said they add a small washer between the barrel and fore end to take any pressure off the barrel. It may be worth a try, especially if the group runs verticaly.
In past posts others have found that experimenting with the way you hold the pistol grip can help. I can't remember their suggestions. You could do a search of the forum.
In order to rule out flinching you could have a friend assist by being in charge of loading. Allow him to load the gun sometimes and not other times without you knowing and you attempting to fire. If you are concerned about dry firing, you could use a Snap Cap. This could be a way to see if, when you pull the trigger, you flinch. The flinching my pull the shots off target. When you attempt to fire without a round in the chamber many times and only a few attempts send a round down range, you might be less apt to anticipate the recoil.
Good luck, Ken