Have I committed a Sharia error in the wording of the marriage contract by repeating the acceptance taught to me by the marriage officiant when he said: "I have accepted marriage to your client, so-and-so, daughter of so-and-so"?

If a man is instructed to say these words in response to the guardian's offer, such as "I give you my ward, so-and-so, in marriage," then the formula is correct and there is no issue with it. It is not a condition for a marriage to have an authorized instructor (mualliqin ma'dhun), and relevant fatwas can be consulted regarding the conditions of marriage.