You need a better stance before you shoot. Lean forward with a foot forward and 70 % of your weight on the forward leg and it won't do that.
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Guns scare me. :)
With your petite frame, you would probably do well with a BullPup shotgun.
Attachment 36789
Attachment 36790That is a Keltec KSG...kind of spendy.
But they make a bullpup kit for a remington that is a lot more affordable, and a lot more reliable! This pic is a before and after conversion: