Here's what I'd do if confined to only 12 yards for practice. I would shoot only one arrow and then pull it. Make my form on each shot as absolutely perfect as I can and really concentrate - focusing my complete concentration on the very center of the very center of the spot I want to hit for several seconds before releasing the arrow.

You'll still need to shoot at varying distances when you can, but if you build a solid foundation with good form, then accuracy will follow.