Change the Size of Your Google Apps Slides

Have you noticed that your Google Apps Slideshow presentations don't fill the screen when using a widescreen display?

If you are interested in filling the display, check out this how to from google:

Change the size of your slides

1. Click the File menu and select Page setup.
2. Select a size from the dropdown menu. You can select from several options:
   • Standard (4:3)
   • Widescreen (16:9)
   • Widescreen (16:10)
   • Custom — If you select Custom, you can specify the dimensions of your slides, selecting the units (inches, centimenters, points, or pixels) from the drop-down menu.
     
     
3. Click OK.

Link from Google: https://support.google.com/drive/answer/3447672?hl=en