As Sphere Mode only summons Ra from your Hand or Deck, you can only use this combo so many times until you run out of Ra's. In that scenario, simply leave your buffed Ra on the battlefield, and hope it doesn't get destroyed (this is why we have Mound of the Bound Creator), or set the game to a softlock by finishing this combo again and leaving Sphere Mode on the field as your only monster until you can combo into a kill (or use Ancient Chant to bring Ra back to your hand from the GY)