i made a rectangle with size equal to window size and when i preview the game there is a margin on the right that means actual window is not what i see in editor.maybe there is something i missed.
humm 
weird…
Is the zoom set to 100%?
How does it display in export?
In the properties panel by default it changes width to fit the screen. Set it to no changes to game size to maintain your aspect ratio therefore fixing the problem. 
