iPhoto printing on custom paper sizes

Hi, this seems like a really obvious one, but I can't get iPhoto 4 to print photos on 3x5 glossy photo sheets. I'm using the hp printer driver, so that may be part of the problem, but in the print options I can't specify the paper size. I can however specify the image size, but when I print with that setting, iPhoto will just suck up my letter size piece of paper under the card and print in the exact middle of the page.

It's frustrating, because the size of the glossy paper I'm using is about a quarter the size of letter size paper, so I want iPhoto to print that, instead of in the middle of a letter size paper.

In the screenshot below, you can see in the preview how iPhoto places the picture. Is there some hidden option? This seems like something that iPhoto should have built in, right?

 

Turns out the solution was obvious after all. Page Setup, duh.