I would get rid of the shelf altogether - I don't think it adds anything to the room. If you want to keep it, paint the moulding/lower wall nearest the door the wall color, and paint the shelf the color of your headboard. That will make the offset look more intentional.

Budget wise.....I agree with @Sammie J

Paint the small area with no shelf over it, the same color as the wall.

Then three small pieces of art centered on the shelf. Center the bed to the Shelf. Add larger nightstands and lamps. With a few changes, you will never know the shelf ends so abruptly.

Use the shelf in another area of your home.