everything depends on the number of applicants in a region. More of them means longer waiting time. Although if an applicant comes from a long distance, he/she is usually given the same day(test/oath) option. There are also exceptions that have their own path though.
write an explanation letter where you can include your calculations apologize and hope the agent will not take your mistake as a misrepresentation. If the agent is going to be satisfied with your explanation withdraw and apply again in case you have required number of days spent in Canada...