BB, I only have v10 to play with.

Can we assume you are working with a Print or Blank Photo document?
If you are using a Web/Presentation document and then Previewing, any print will be why the browser has visible. I shall discount this.

As @handrawn says, use Window > Show Print Borders.

The next thing you need to do is check Page Size against Print Options.
It makes sense to print to the size of your physical sheet of paper - US letter, A4, etc.
Xara is clever as it knows to print sideways but is is best to first tell it your paper size explicitly in File > Page Options > Paper size.
If you then try to Print, you should see Automatic fit OK.

You are now in a better position to hijack the settings and manually adjust margins and scale to meet your needs.

Acorn