If this is the case there is probably something wrong with your background resolution. Make sure the image used as a background is at least the same resolution as the desktop it's running on.
A bigger background is possible, if you select "touch background" under the page's properties in "markers & images". Users will now be able to zoom in on the background. To make sure the markers are scaled proportionally, make sure each marker on the page has the "scale marker by background" option checked.