It does look like you have a wide bed. When you get a chance measure the rear fenders. Wide bed fenders are 10" instead of the 12" that the other beds use.
Let me look a few more things up as well.
Ok more info, the wide bed does not have the square in the bed. The inside dimensions are 60" L x 46" wide at the floor ad 54 1/4" at the top of the rails. Top of tailgate from bed is 14" and top of the front rail is just over 17".