12 isn't too much if you only train chest once a week but you may want to change the routine.
Instead of 3 of everything do 3 each of the mass builders then go to 2 each of the assistance exercises for a total of 6 assistance sets.
Ex. 3 bench press, 3 incline press, 2 dips, 2 db flyes, 2 cable flyes
If that's not enough then you're doing something wrong.