Lurch, make sure you file a draft on the sides of you buttplate tang before you inlet it. FIle the edges smooth and crisp, and bevel the edges in toward the center of the stock.
With the gap on the top corner*, you may need to saw a little off the end of the stock, shortening the pull a tad. That plus hammering the brass to reshape should get you what you want.
* if that dark spot is just a shadow, I would not follow my above advice.
Your camera is focusing on the background. The light is coming from behind the gun, so the autofocus is latching onto the first detail it sees, which are your tools. You can set your camera to 'center focus', so it will focus on what is in the middle of the viewfinder. The camera needs something to auto focus onto, a detail, a line, something it can distinguish from smooth wood. Stick a little piece of tape on there, and the camera will focus right onto it.