How to get rid of white border

[Adam38232234imp5]

I was working in Lightroom and must have accidentally hit a wrong button because now all of my photos have white borders. They don't export that way so it must not be actually a part of the photo but simply something wrong with the View settings. I've looked everywhere in the program and tried to research it but am unsure of how to remove the borders.

On a sepereate note but that occurred at about the same time, in the Editing tab my program suddenly only lets me have one subsection open at a time meaning I can't have Light, Color, Effects, etc. all open at once to quickly edit photos. When I open one it automatically closes another. I'm wondering why this is. 

[Ian Lyons]

You must have inadverently changed the background colour. You can revert back to your preferred colour by right-mouse clicking on the background, then choosing whatever colour from list that you prefer. I've attached a screenshot that might help.

[Jim Wilde]

On a sepereate note but that occurred at about the same time, in the Editing tab my program suddenly only lets me have one subsection open at a time meaning I can't have Light, Color, Effects, etc. all open at once to quickly edit photos. When I open one it automatically closes another. I'm wondering why this is. 

By @Adam38232234imp5

Click on the tri-dot icon below the edit tools in the right-hand edit tool-bar and click on "Single-Panel Mode"  to turn it off and revert to your normal behaviour (multiple panels can be open at the same time).