When you open the Print dialog in Aperture, you'll see a preset named Mini Size Book. Please note that you should only select this option if you're working with a Mini Book template. This preset does not scale down a full-size book layout, but rather sets up your printer for the paper size needed to print a Mini Size Book layout.
If you select this preset in the Print dialog while working with a full-size book, your images will appear cut off or they may not appear at all. Before you print a book, make sure that you select the print preset that corresponds with the size of the book you've laid out.