What are you playing the movie with?
If the source is not connected with HDMI you would need to set the aspect ratio to 16:9.
If the movie is not 16:9 then you would see bars either on the sides or on the top and bottom of the screen. Most TVs have a button on the remote to either stretch the picture or cut off the sides to get the movie to fit the screen. Often looks bad and you lose some content.