Most ballcock type tanks have two adjusting screws at the water inlet part of the ball rod. The screw on the left is to adjust the height of the ball, to keep it from hitting the lid. The one on the right is to adjust the water height in the tank. This should be 3/4" below the overflow. I would have gotten rid of the ball and replaced the inlet with a Fluidmaster 400A fill valve.
if you have never made a mistake, you probably haven't done much.