Are you sure your index cards are 5 x 8? Usually they are 3 x 5 or 4 x 6.
You don't need to change the paper size; you can use letter. It all depends
on how and where your cards are fed to the printer as compared to letter
size paper. If your index cards are fed long ways, set your printer for
landscape and if fed short ways, set your printer for portrait. You need to
design the Access report based on which side of the printer the cards are
fed. If your index cards are fed on the left side, design your report to
appear at the top left; small left margin. If fed on the right side, large
left margin to make the report come out on the right side of the paper if
you were printing on paper. Add a page break(from toolbox) after each record
to get one record per card.