I did try to flatten the piece by applying more Seal Coat on the cupped side and putting weight on the opposite side. I left the weight on the piece for approximately 24 hours. When I removed the weight the piece was flat. However, as the day went on, the piece slowing returned to the cupped state. It was improved at all. The cup was the same as it was originally. I didn’t try to wet it again.
Oh well, I considered this all practice and experimentation. It wasn’t a piece that I was going to display or incorporate into a box or some other object.