Perhaps replace with new then. Its reusable, adaptable and will conform to whatever shape you need.
Also make sure you key/scuff the outside of the new pot before sealing it in to allow the sealant to bite into it. Sounds obvious, but i found my one had been previously installed as a lovely shiny new pot. Subsequently the adhesive didnt stick for long. Another good tip is to screw it to the hull from inside, as this helps provide additional supprt to cope with the torque of regularly tightening the pot lid.
I have tried putting the hull in our pond with the keel weight in approximately the correct position. The water line came up to less than 10 mm above the bottom of the stem and just on the bottom edge of the transom. On this basis I think the weight will probably be OK after all, provided I fix it in the correct location longitudinally on the centreline. However any advice would be gratefully received.