What if I find an If the error is in the original census document:

error in the original census?
- a surname note provides an alternate surname spelling and allows the members of this family to be identified in the result of a search done on this alternate spelling. When entering a surname note, indicate if it applies to the entire family or only to this individual. Also, please include the bibliographical reference to the source that corroborates the surname provided, and if applicable, add an associated note.

You will find much more information on this at Surname Notes

-for a discrepancy in the given name, gender, and/or date of birth - an online or off-line birth record link is the preferred way to annotate the correct information.