Hey experts, question about issue with my 12 ga Mossberg 500 (w/ slug cantalever barrel and simmons scope)

Last season I was comming out of the woods and my sling broke, I caught the gun enough that only the barrel hit the ground like this ( \ ) over my back. It plugged with Dirt/gravel/mud...and hit fairly hard. I then gave the barrel a quick wipe down, rag through the barrel with water..then dry rag...and continued to go hunting in the afternoon. I went to sight the gun in to confirm I did not bang my scope out of wack...and it won't shoot accurately. I shot about 12 bullets off sandbags etc...and it won't hit. Some dead center...some way out, no constant grouping. I am willing to change the scope, although I believe the issue may be the crowing in the barrel from what someone explained. Can anyone give me insight on what they believe it could be...and what a repair would cost ? Thanks in advanced.