Sorry your hatch didn't go well.
Golden 300s are a hybrid line. You wouldn't expect genetic problems with a hybrid like you would with a purebred line. I think most people don't breed them at home because the sex-linked coloration only holds for the first generation. With out the...
Were the membranes really dry with the eggs that hatched? If so, you might have a shrink-wrap situation with the last egg, and it might be worth helping it hatch.
I am hesitant to assist much. I assisted a really late egg once. The duckling had genetic defects. It is really hard and sad to...