Just re-read your OP and realize you're trying to resize in the Print menu. Instead, try this: go to Image > Image Size and change your size there. If you're getting fractions of an inch, it's because unless your photo is a precise square, Photoshop is "constraining proportions" to maintain the aspect of the photo and not distort it in one direction or another. This link may help you understand it:
Work with a COPY of your photo, NOT the original!!
Hope this helps, it's easier than it sounds.