that was my old technique, training wheels if you will
because your hash patty will break up into chunks if it's too wet or too thin.
Now I just use the microplane grater and a teflon coated baking sheet. If you use a non-teflon baking sheet, or anything else really, the hash will stick to it and you will have to deal with that. As the broken up hash dries I move it around and "cut" up the clumps with a plastic card, lol, real high tek
My tip for your first run is to not over agitate, do it gently and slowly for a longer amount of time. Assuming you are hand stirring. I used to hand stir for a hour with a large wooden spoon, tag-team with a buddy. The more ice:water, the harder to stir, but colder is better so do some arm and back stretching.