I wanna print on a custom paper (13x13 200gm Glossy) with a custom print form in Windows 7. With this configuration, the result is not what I've set. What I'm getting is an 11x11cm, top left aligned picture. My printer is the HP LaserJet Pro 200 Color.
Your screenshot indicates you have a specified margin of 1.00cm on all four sides. If you are setting the margins at zero and they are defaulting back to 1.00cm (or to 0.8cm as indicated by your stated 11.4cm² result), it may be that your printer is not capable of printing without a minimum margin of 0.8-1.0cm.