Gotta be careful with this one. If, by "balance point", the coach wanted to to "stay back" and "stop at the top", then that was bad advice. Pitchers need to get it going and eliminate any extra time they have in their delivery - like the extra time that allows them to spin out. You want your timing such that you can only get to the squared up position at release.
Now, if all the coach meant was that you weren't maintaining balance, then that was ok. In this case, you need to pay attention to what your head is doing. It shouldn't move up or down, back (toward 2nd base), or side to side. It should only move towards the target. I teach my kids to picture their head as a bowling ball in a gutter.
It sounds to me like the drill the coach gave you are "step behinds" - not "cross overs". Step behinds are more general in nature - their only emphasis might be in building up momentum quickly. I have my kids do them for warm-ups. But they are not specifically geared towards balance problems. It really sounds to me like you had too much head movement, were rotating the shoulders too soon and too much, falling off to the side, and all of this was creating the appearance that your were slinging the ball and not staying behind it and throwing through it. If this is a correct guess, then I really think you need to work on minimizing head movement, getting the upper arms into an opposite and equal position at foot strike, and getting down the hill a little quicker so you don't have time to open up too soon or too much. Work on the head first - it's a big factor in the rest of the delivery.