VideoScribe is set-up so the canvas is 16:9 aspect ratio so when you set a camera position it will be shot 16:9
With the ruler it is not a setting that can be changed i'm afraid but it is set to be translucent so you can see the edge of the canvas and put images to the corner. VideoScribe will hold that camera position once it has been set. Just be aware that if you resize the VideoScribe window (Maximise from part-screen or visa-versa) that you can see more/less of the canvas so it looks like the position has changed. It hasn't however and if you double click on the element in the timeline it'll revert back to the original camera position on the re-sized screen.