I think your tiller is looking good now, but I like to leave my tips a bit stiff, just like in your last picture. But to answer your question, I would just keep removing wood evenly now, making sure your tiller doesn't do anything funny along the way. If you want to get exactly 50lbs @ 28, you could tiller it to 50 @ 27 and the last 2 or 3 lbs you'll lose from final sanding and shooting it in, which will put you pretty close to 50 @28.