There's kind of a trick you can use here to keep the whole photo. Size your croping tool to 8 by 10 at 300 dpi then drag till you reach the edges of the shot. You'll still see the little sqaure dragging handles on the corners. Drag those (try different ones) out BEYOND the border of the existing shot till you have everything you want on the 8 by and some blank space on one or both sides.
Fill the blank space with either copied sections of the existing background, or solid color, or a pattern, whatever works for you artistically. Then when you send off the sized print it should contain everything you shot.
(Handy extra tip) On this shot you have blank wall to either side of the model. After you've dragged the frame where you want it, to fill the empty spaces at the side use the rectangular marquee tool to copy a slice from top to bottom of the frame copy that slice onto it's own layer click edit> free transform and just drag the wall out to fill the space.
You may need to feather the selection a little, you may also need to blur the side some but you will definitely be able to keep eveything you shot on an 8 by 10