It sounds like an Image Size issue. Use Alt Ctrl I to check what the physical size of the image is set at. Then, if you have enough pixels, uncheck 'Resample Image', and adjust the 'Document Size'. You might also have a Fit to Paper option in the printer properties.
But did you also actually change the image size? What are the pixel dimensions of your image (so many pixels wide by so many pixes high) and what is your print resolution (in ppi)?
If you only change the paper size and/or the canvas size, the printer will just keep printing the same size image centered in your paper size, of course.
Wo Tai Lao Le
…Use Alt Ctrl I…
On the Mac (which the OP says he's using) that would be Option+Command+I.
One has to remember that the forums have been merged…
… option in the printer properties.
Er… that would be a setting in the printer driver dialog box. Printers don't have "properties" in the Mac world…
I found it... Under paper handling there is a box that says 'fit to paper size' or something like that. I needed to check that even though the image was already about the right size. Without checking that the driver was shrinking things down for some reason.