Print preview and Printer-friendly version look different
You have two separate stylesheets.

The 'preview' stylesheet needs to be configured in the CMS. You just enter into a field something like 'print.css' and create that file in your theme folder. This is nothing different than a typical stylesheet you would use anywhere else on the site.

The actual 'print' stylesheet (what you get when you press the print button) that you have declared in your .info file will style the resulting print.