You want to use the camera tools at the bottom of the toolbar. The left one moves the output area around and the one next to it zooms in and out. Just zoom out to cover your whole scene and then move it to frame it correctly.
The blue square is the edge of the camera's frame. If you want to change its size in the editor window, you can use the Zoom tool at the Workspace tools, or the mouse's wheel, if you have. In the final material you will see only the parts inside of the blue square. This is independent from the size of the viewed part in the editor window, so you must set the blue rectangle to the right size around your drawing. To do this, use what alano wrote above.
I think you may have used the 'Workspace' tools rather than the camera ones - the camera tools are the slightly pinkish ones (with pictures of a camera on them). Second row from the bottom.
