Thank you for your message.
The black bars on the side of the screen are caused by the screen resolution difference between your Host and Viewer. Unfortunately, Remote Utilities has no control over the screen resolution of the remote Host, so there's currently no way to get rid of the black bars. The only solution we could suggest is using the "Fullscreen Stretch" view mode. However, we plan to implement a feature that would allow adjusting remote screen resolution within your Viewer, so that it's possible to match up remote screen with a local one. Hopefully it will be available in one of our future updates, but there's no specific ETA on it yet.
Let us know if you have other questions.