Unfortunately, your understanding is a little off, and you are not quite
UK citizen yet, being born 2 days early!
If you were born before Jan 01, 1983 (like you), you had to have a
father who was born or naturalised in UK, for you to
automatically be a UK citizen. After that date, either your
mother or father had to be born or naturalised in UK, for you to
automatically be UK citizen. These would simply submit a passport application.
Since 2009, for those, like you, who are born before 1983 to a UK mother, a path to citizenship was provided, however you must first register (costs ~500 pounds), undergo a background check, and attend a civil swearing in ceremoney.
Then you apply for passport.
Look for form UKM on the british passport site.
http://www.ind.homeoffice.gov.uk/britis ... ishmother/