Legal Question in Real Estate Law in California

I assume that you are the borrower (rather than the lender) and that the error is confined to the parcel number itself, rather than any other information describing the property such as street address or legal description. I would gather all the facts and make an appointment to see the lender's law department. They should prepare either a correction notice or a corrected deed of trust for signature and recordation, without cost to you. Then pay a visit to the county assessor and explain what has happened and ask them what further steps are necessary to get your property taxes in good standing.