That target is a very helpful item to keep nearby. I have copies for both right-handed and left-handed shooters posted in each shooting point at a range that I administer.
A complication is that some variations of that visual aide will say "too much or too little trigger finger" as a cause of shooting left. Which it is depends on the size of the shooter's hand, length of fingers, size of the grip, etc. Sorry to complicate this but there is a lot going on in the hand when the trigger is squeezed.
The target does give you a place to focus, though.
Also...have you established your natural point of aim (NPoA) when shooting?
I was shooting consistently left at a match when I'd just started with the Free Pistol. A helpful coach, standing behind me, told me to move my feet. Voila..the shots moved to the center.
Is the gun placed securely into the web of the hand so that it aligns with the bones of the forearm?
"Only hunting and mountain climbing are sports. The rest are just games." - R.Ruark
NRA Life Member