Premiere Pro - Exported MP4 file won't play across whole widescreen on playback

[lesliek1]

I have set the sequence settings, export settings and AE settings to 1080 x 1920, my monitor setting is 1080 x 1920 and when I edit I use the entire program screen and that is set to "fit".  When I play back a MP4 file, it will NOT play across the whole screen; there is black background on both sides of the video.  I expect that on some of the images (this is a montage comprised of many stills and some are vertical), but not all images.  Thank you for any help you can offer!

[Ann Bens]

Which player are you using to view your mp4?

Did you take in account the buttons on the bottom of the screen?

Are you using more than one monitor?

[lesliek1]

Using VLC media player, my laptop is connected to a larger monitor 

[Ann Bens]

What is the resolution of this larger monitor.

[lesliek1]

These are the specs for my larger monitor