Thanks for your reply, however when I resize this way, or by using the resize option with only the top layer selected, the background is still only filling half the canvas. My issue is that on import the canvas size changes to fit the new picture instead of being locked to 800x800 as I set previously.
I figured out how to resize the canvas again after import and so my issue is resolved but any suggestions on how to lock the canvas size so it won't change on every new import?