It is almost impossible to give good marksmanship advice for specific problems without being there in person to see what is actually going wrong, but I think the most likely source of your problem is being too tense. You don't have to keep the weapon solid as a rock the whole time, just relax and when you are not actually taking a shot, let the muzzle drop (just slightly, just enough to loosen yourself up). You might also be pressing the butt plate too firmly into your shoulder, it only needs to rest there. Some folks with more experience in marksmanship instruction are on the forum, and if this doesn't help you, I'm sure that they will be able to give you a hand.
No boom, no boom, no boom, Amen.