Certificate sizing

I'm trying to create a certificate that has images, namely a background image. It looks fabulous on the screen, but when I download the pdf with the tokens filled in, it is much too small. I've tried every size ... resizing the background image and replacing the token with css, but the resulting pdf is always the same size and too small. Any suggestions? I've tried to look for support from the certificate module writers, but that seems nonexistent. Thanks, Missy