DVD movie won't fill screen in full screen mode of DVD Player app (through USB Superdrive)?

I put in the DVD in the USB Superdrive.

The app opens. Everything looks fine. Then I go to full screen mode. And the movie is not in full screen.

There is clearly space to fill in by zooming in.

This is not a matter of aspect ratio. See the image included. The cursor is clearly in the black bars.

How do I zoom in? Unfortunately VLC player has too many visual obstructions.

edit: screenshot is censored of course, so I had to make a pic with my phone.