To fix this problem you need the "Arm Rigging" to be the same canvas as for the Art program itself on whatever streaming software you're using!
Right click -> Transform -> Fit to Screen FOR BOTH DISPLAYED SCREENS and this should fix your issue :] happy arting!
edit: if its still funky looking go under 'Preferences' in your drawing program and mess around with the cursor and other settings it offers. I am currently doing that now and it's been improving!
OMG edit 2....: Okay so this was a easy fix. What I did is SLIGHTLY adjusting the art program and leaving the Hand+Pen to be its full screen OBS size [which mine is 1270x720]. And it's fixed!