what might work better for you is to add the image plane to the camera.
in the viewport click view at the bottom you see image plane, and then click import image.

The reason why your image won't fit nicely onto the plane is because of the UV's. The uv's are square for your plane despite the fact that your plane is of a non square shape.
To cure that you can go to create uvs ---- Autmoatic Mapping, OR Planar mapping, but in the planar section you need to choose from which direction.

Hope that helps.
Keep in mind that even in that setup some of your image will be cutoff. I think you'd want to keep the settings how you have them. There are things far more in depth at work here.