You were 30 yards away when you aimed and fired the longgun. Strictly I should have given you a -20 penalty for being at long range (24/48 on a Firearm) but you nailed it anyway.
Blunderbuss range is 32. If you move and fire this turn, you'll be at 24 away, which is comfortable enough to hit quite a few of the enemy with the spread.
But that said, I will requires damage rolls for every hit individually; as the blunderbus is more of a spread of damage distributed among a group, and not a wheel-of-fortune spin that can fire either confetti or antimatter.
You may keep that 12 as the first damage roll, however.