Hi! I'm not totally sure because I don't use rpg maker MV, but my friend guessed this;
If you want your image to fill the screen without looping, you should: Set your game resolution to 1920×1080 using a plugin like Yanfly’s Core Engine. Use your 1920×1080 version of the image as a Picture or Parallax Background. Make sure the image is centered or stretched appropriately using MV’s event commands or plugin settings.