Must one pay for the extra candy found in the bag, knowing that the candy is sold by weight and not by piece, and that the price originally paid was by weight?

Your question contains its own answer. As long as the sweets are sold by weight, there is no problem with the number of pieces varying according to the specified weight, even if there are two extra pieces. Such a matter is customarily overlooked, because the rulings of Islamic jurisprudence excuse minor discrepancies to alleviate hardship and grant ease to people, for what is insignificant is as if it does not exist. It has been noted in your previous questions that there is some obsessiveness and undue strictness.