Matt is right on follow through.
You won't improve anything until you shoot up close, start at 7 yards. This will allow you to easily maintain the same sight picture each and every time.
Once you have a nice, tidy group, then you can set to work about identifying what you're doing incorrectly.
95% of the people with Glocks say "It shoots low and left" (anticipating the shot recoil and pushing the trigger/right hand shooter) or "It shoots low and right" (anticipating recoil and pulling the trigger into the shooting hand/right hand shooter…both are swapped for a lefty).
If you have standard Glock sights, keep your circle centered in your box the whole time you slowly squeeze the trigger to the rear, focusing on the front sight.
FWIW, ignore the correction chart until you can get groups half the size of your palm…then refer to the chart.
After you have 7 yards mastered, move out to 10, then 15, then 20, and back out to 25.