How do I get the full wide screen in this window?

Try basic video editing techniques |

The Program Monitor window sets itself to the size of the sequence that you're working with. Perhaps your video was shot with this aspect ratio or you have your sequence in a different sequence than your video size?

I would highlight the video that your working with then go to the information panel and check its x y frame size, then highlight the sequence in the project panel (bars icon) and see if it is the same frame size.

If the frame size on your video and sequence are the same then your video was not shot wide screen.