Responsive Design

I built out a new website with the new websitebuilder because I wanted a website that was, "Responsive" meaning that the page will adjust so that it appears to fully fill the screens regardless of the screen width, however, it's not working out.  It's fine on the screen in my home, but in my office, the page is much too large.  Any suggestions?  FYI - I have not published the site but am only working in the preview mode, perhaps that the problem?  Thank you.