Looks like an artboard inside another artboard. What happens if you open the artboard panel? Is more than one artboard shown?
To my eyes that square appears to be the only artboard, in which case you can resize the artboard (Window menu > Artboards) to match the image, scale down the image to match the artboard, or hide the artboard (View menu > Hide Artboards).
It looks like your artboard, either reduce your artwork to size or fit the artboard to the artwork..?