The lack of a master builder is the problem that a lot of people have when they first try to complete Puzzle 12! There is an Island Event that washes more debris onto the beach, but it takes more than one of those to create a master builder. You could wait to see if the beach debris shows back up again enough times to train a new master builder. I know of several people who have successfully used multiple beach debris events to train another master builder and complete puzzle 12! Or you could start a new game and use your experience to try some different strategies! You don't have to wait until the end to complete Puzzle 12.