I've hunted ducks and geese for some years now, even back when there was no such thing as steel shot. Ahhh...the good old days! But none the less, we've gotta go with what we got.
Which leads me to a question for you, as one of the previous posters also asked, what type of ammo are you shooting? Steel? Tungsten-matrix? Hevi-shot? Assuming you're using steel, part of your problem may the range at which you're taking shots. I wouldn't take a shot much further than 30 yards out, preferably closer. It can be tough to discipline yourself to do this, especially when there's a flock of honkers just 50 yards out. Then again, maybe it was only a big deal for me, being used to using lead and a tight choked gun.
I would also suspect that your swing and follow through needs a little work. Swing onto a bird and swing past the feet, tail, body, neck, head, bill, and BOOM! You can practice this by picking an object hanging on a wall as your "target," then practice mounting your unloaded gun and swing onto your "target." If you have a snap cap, (I don't, so I just say "BANG".) you can dry fire at the point you would normally shoot, and swing beyond your shot. Keep your cheek against the comb of your stock and keep swingin'!