I'm guessing the confusion may be that while you may have 93 balls in your "inventory", that likely they are of different types than the one you are currently playing? You must finish the game with either the EXACT same ball type, even down to the color (one ball rule), or be switched to the Starter.
So for example if you start with only 1 Cally L33 ball you will get a prompt to buy more at the first tee, then if you get down to last hit on it will get another prompt. I believe even if you hit it in the water you may get a chance to buy more before switching back to the Starter. It doesn't matter that you may have 93 "other balls", only what you started the game with.