In the Page Setup (lower left of the Print Module) you can set up the paper size. The 3800 driver lets you select a custom paper size so you'd input 12x13. On the first screen of the Epson driver toward the bottom of the screen are the Paper Settings. On the right is a button labeled User Defined. Click that then input the paper dimensions you want to use. Back in the LR Print Module, you set up your margins in the Layout Panel (right side of the Print Module) to place the image where you want it on the paper. If you want it pushed to one side to allow for binding or hole punching, you would move the slider for the appropriate margin (e.g., left side) so that the image printed to the right side of the page.