How do I fuse a selection to the side of a picture to effectively length it?

[Blighty]

1. Enlarge the canvas size.

2. Make a selection of the right hand edge (see the selection border)

3a. Copy the selected area
3b. Paste. Right Click on the Floating Selection and "To New Layer"
3c. Use the Flip Tool to flip this new layer horizontally
3d. Move so that the edges line up with no gap.

4. Use the Scale Tool to stretch the new layer (Keep Aspect must be unchecked)