I am confused? You are trying to print on a letter size ,8 1/2 x 11, sheet of paper?
Whatever, it is just a selection in "printer settings". It may be the default setting and you need do nothing!
In printer settings there is a box to select "borderless", too.
In Photo Shop, select print under the File drop down. At the top right there is a box showing your printer and below is "Printer Setting". Click it. You will see a window that let's you select any number of things including Printer Page Size. Also is Additional Settings which has Borderless printing.