As long as he's alone and not getting stepped on by any other ducklings, I'd leave him in there for now.
It looks like he has a protruding navel. The yolk is still being absorbed and the navel hasn't completely closed yet. I've had quite a few ducks and goslings hatch with their navels looking like that and all have made it. If it's getting smaller, that's a good thing.
Whatever you do, don't try to pull him out of the shell, it could cause him to bleed to death. Keep him as quiet and still as possible. He'll finish the job when he's ready. The laying still and not moving around much is normal to at this point.