What is the ruling on exchanging gold for gold with the payment of a difference, and what should I do if there is a sin involved?

It is impermissible to sell old gold for new gold with a payment of the difference according to the majority of jurists. Whoever does so must seek forgiveness and annul the transaction if possible; otherwise, they must repent and seek forgiveness. Some scholars, however, hold the view that it is permissible, seeing that a gold ornament, through craftsmanship, becomes a type of commodity. Thus, it is permissible to sell it for its like with an increase in exchange for the craftsmanship. This is the chosen view of Ibn Taymiyyah and Ibn al-Qayyim. According to this opinion, what the questioner did is permissible.