Margins - Read Carefully! Start by setting all margins to 0.15" at minimum. You can come back and adjust if necessary, but do not go below that number. Now name and save the new paper size for later use.
Custom Paper Size Using Photoshop CS3 / CS4 Mac, for Red River Paper greeting cards, scrapbook 12x12 sheets, panorama printing, and other special projects, you need to define a custom paper size in the Epson printer properties. This may take some experimentation but is necessary. Define a custom paper size. Important Tip - the smaller paper dimension is always the width. The larger dimension is always the height.
Canon Note, most Canon printers can only print up to 23.39" long. Setting your paper size over this maximum will likely cause random print errors from OSX. Special OSX error fixes, newer OSX versions, 10.6 and up, have issues with handling custom sizes correctly. To begin, go to file print. Choose your printer from the Printer drop down menu, then click, pAGE setup, pAGE setup dialog. Choose your printer from the "Format For" drop down menu.