You've spent hours for years, kinda hunched over with 1 arm in an isometric upright row, and the other in a short-range horizontal row. Of course you are a little out of whack.
You'll need to spend some time working both sides through all kinds of ROMs, equally.
Try 1 arm pulldowns, left side first.
1 arm rows, lefts side first
1 arm shrugs, knuckles out to the side, right arm first
Really try to feel the stretch at the "bottom" and the squeeze a the top. Focus on full range of motion, and time under tension, not poundage at first. Train your two sides to feel the same.
This always makes my scaps feel Yo Yo Ma-rvelous
Good Luck! Happy Easter!