If I start shooting L or R, I'll take a strip of 1" wide tape, painters tape or whatever I have layin around and put a piece vertically on my bag target and shoot to hit the tape. I dont care so much about high or low, a long as the windage is the focus of a practice session.
I find for me, if I'm missing L or R, plucking on release, or not holding the bow still is usually the culprit. Although back tension can mess me up too.
Do the tape drill until you're hitting or darn close to it every shot.