Thanks for your reply! What happened is the first help I found was not the page you linked to above. And well... there is lot of bad help. After three hours I found the page you linked to above and... all is not good.
Always found Prawn way to "heavy" (a lot of learning for the amount I needed it). This way is amazing and fits my needs perfectly. Probably a "proper" way to do it but I had to get the "bootstrap" css from the CDN and turned on the option to print the background.