Exporting for web without trimming

I've created a custom page size 815px X 315px which is perfect for facebook covers.  When I export to .jpg corel trims the document to a smaller size ultimately hiding many words.  The "selected only" box is unchecked.

If I export to .png it does not trim the file or image.

What setting should I look for so Corel exports the page size exactly as it is?