Maybe on a Mac system, it has different options for scaling during printing.
More likely, you'd need to develop your own layout where you have scaled the layout to fit on the index cards. If your index card stock comes with an Avery Number you may be able to use the labels option in the New Layout wizard to set up the basic layout to which you'd add what you want to see printed on the cards.
Yes, that makes sense. I'd have to think about it in more of an "address label" way.