You may be a bad putter or you may not be…
Hitting 9/9 greens is great 20 putts is not but none of that says you are a bad putter. If your first putt is from 40 feet and you 3 putt, it’s not the putter that is the problem. This is one of the problems with “center of green” If the green is 40 yards wide, pin on left and you hit right third of green, which may be only 5 yards from your target the upcoming putt is going to fall at a distance that 3 putts are common.
Basically until you have proper data it is hard to determine strategy or what facet of your game is not working.