While you are not responsible for the contents of the document being notarized, you are responsible for the accuracy of information contained in the notarial certificate. So if you make a mistake on a notarial certificate, you are the only one who can correct it.
The solution is simple. Cross out the incorrect information, write in the correct information, and initial and date it. Anyone reviewing the certificate later knows that you are the one who made the change. You should also note the correction in your journal so there is a record in case questions arise later.