Can I convert my king size, wheatback headboard to queen size?

Please post a pic of your headboard & we'll try to help you.

Not knowing what kind of headboard you have, it's hard to say if you can reform it. Here are some pics of King headboards with Queen beds that don't look bad at all. I recently sold my footboard, as they are way out of style at the moment.

https://www.google.com/search?hl=en&tbm=isch&source=hp&biw=1361&bih=668&ei=242hWomhMoXQsAXFlqbIAw&q=Queen+bed+with+King+headboard&oq=Queen+bed+with+King+headboard&gs_l=img.3..0.1706.1706.0.4325.2.2.0.0.0.0.81.81.1.1.0....0...1ac.2.64.img..1.1.81.0...0.EZodIbEOrVY

There are a lot of information about queens to king, but very little on the opposite. I did find this site and read it, it may help: https://www.hunker.com/12001679/how-to-convert-a-king-to-a-queen-size-bed

A king size should be 76 inches and a queen is 60. So, if you can cut 8 inches from each side and keep the look, I would say yes. You could screw it directly to the wall or attach it with cleats.

You could keep headboard as is & add floating shelves with legs only in front. Use that space for some sort of nightstan, either one you have or homemade. Perhaps, depending on center design if any, you could cut out the desired length, then glue & fasten on the back finished size. Fill the cut area with wood glue then paint or refinish.

I can cut it down and make it a queen size. Unless you have already resolve your issue