I guess that's why it's posed as a question. You don't have to say "I do."
Anyway, if you're 16, the correct response to a marriage request is 'No.' Unfortunately, it seems that Lois did end up getting married a week later, despite her initial reluctance.
The Ottawa Journal - May 1, 1971
Girl Says 'No' At the Altar
SIBSON, England (UPI) —Radiant and demure in white lace, Lois Elliott walked down the aisle on her father's arm as the organ intoned "Here Comes the Bride."
"Wilt thou," said Rev. Frank Best, "take this man to be thy lawfully wedded husband, to love and to cherish 'til death do you part?"
Lois, 16, smiled at Mr. Best, at her father and at the groom. "No," she said quietly. Then she turned and walked out of St. Botolph's Church.
Lois offered no immediate explanation for her change of heart. But her father, Barry Elliott, said he thought a chance remark by one of the groom's relatives "may have upset her."