Your social security card would have your name listed as the applicant filed it. If the provider used one of your last names as a middle name, then that is what they recorded. The last time I filled one out there was a separate section for middle and last names.


Do you have a middle name?

from what I can find regarding Washington birth certificates, they do separate middle and last names on the application.

I would contact the Washington department of vital records to see if they retain a copy of the application for an original certificate of birth and see what it says on there.