Did the marriage take place by the young man's saying "yes" in response to the young woman's question, "Will you marry me?" And is the young man's apology to the young woman sufficient to return grievances as a condition for repentance?

A marriage is not legally concluded except in the presence of the woman's guardian (wali), two just witnesses, a dowry (mahr), and a formula indicating the marriage contract. Therefore, your agreement to the girl's statement "Will you marry me?" is not considered a legally valid marriage.