will my game fit the size of the screen of any device that uses it?

I know that it has probably already been asked, but will my game have a black border around it?
my game is 800 x 800 pixels, so will my game fit exactly to my android screen, or not?

What size is your screen? It’s not perfectly square in any case. It is important to keep Aspect in mind when making your game.
In the game view window, click where it says ‘Free Aspect’ and you can customise your View. 800x800 is not an option for any screen, though.

The game will not have a black border but will either become deformed or clipped.

When I try a larger screen size it actually gives me a wider FOV angle on my game and smaller screens give a narrow FOV.