Why does my Zoho Sites webpage appear with a frame around it and gutters on either side - doesn't fill the browser

Why does my Zoho Sites webpage appear with a frame around it and gutters on either side - doesn't fill the browser

When I publish my webpage the page layout doesn't fill up the real estate of the browser - the page appears with a big frame around it and vertical gutters on the left and the right.  I want my webpage to fill up the full horizontal page.  See attached screen shot.