Everything looks like it should work, and the settings tested correct when I made a test drawing.
Check for objects on hidden layers, as that will cause the problem. This caused the issue when I tested for it.
One other thing to check is to make sure that there aren't any hidden or non-visible entities in your layout outside of your titleblock that are preventing the drawing from scaling to full page.
One way to check that is to select everything then deselect the titleblock and contents.