Canon iP8720 does not allow me to select 5.5 x 8.5 paper size.

How can I print a 5.5 x 8.5 image on a 5.5 x 8.5 sheet of photo paper on my Canon iP8720? Borderless. There is no selection for that size paper. I'm using Photoshop Elements 5 to print from.

Thanks, Russell