Sharpshooter feat not tracking on rolls

My sharpshooter feat -6 on ranged attack roll and my +12 bonus is not working. It never subtracts the -5 from the roll, not adds the +12 to the damage. Then when i correct franz he just smites the opponent. I hit an opponent for 15 damage with sharpshooter's plus 12, it should be 27hp damage leaving the merc at 3hp left. I ask franz to correct it and he just subtracts 15 again instead of the 12 from sharp shooter, killing the merc without giving the merc a turn.