I'm not aware of any epson sheet paper that is 13X18, so I'm not sure what you are really trying to do. If you want to print on Super A3 sheets which are 13" X 19" in size, and your software isn't pre-configured with that paper size as an available option, you should be able to create a "custom paper size" of 13 x 19 and then print on that paper. Simply size your image to be 13" X 18" and tell it to print onto your "custom size" of 13x19. It should print with approx a half inch border on the two ends. If that is what you're trying to do.
I'd also contact your software maker and tell them to get their act in gear and pre-configure Super A3 paper size into their next update.