Topped shots / thin shots and even fat shots are most often caused by moving off the ball. For most people, that's because they sway backwards rather than turning. Once you sway off the ball, your body has to try to make a move to get you back in position before you hit the ball. If it's successful, you hit something resembling a decent shot. If not, you hit it thin, fat, off the heel/toe, etc. When I hit a really bad shot, the first thing I fix is to make sure I'm making a good turn and not swaying. Give it a try - I'll bet you'll find it helps get you back on track more quickly.