[Lt. Skrumpledonk Ret]

You're pulling the trigger too slowly. Try a quick, crisp jerk and equally quick release. If you squeeze and hold the trigger, another round will go off as you release.
Stick the very bottom point of the butt stock in that nook in your shoulder, right below your clavicle. It'll look odd. Hold it by the magazine, pressing your elbow into your ribs with your left foot at 12 o'clock and your right foot at 6 o'clock. You can hold the rifle in that shooting position all day with one hand.