All 3 courses need to be taken to have antibodies in the system. Your results indicate you are not exposed, but you do not have antibodies.
You need to contact your doctor, before not taking the remaining doses.
Here is a snippet from the precribing information : http://us.gsk.com/products/assets/us_engerixb.pdf
Booster Vaccinations: Whenever administration of a booster dose is appropriate, the dose of ENGERIX-B is 10 mcg for children 10 years of age and younger, 20 mcg for adolescents 11 through 19 years of age, and 20 mcg for adults. Studies have demonstrated a substantial increase in antibody titers after ENGERIX-B booster vaccination following an initial course with both plasma- and yeast-derived vaccines. (See CLINICAL PHARMACOLOGY.)
See previous section for discussion on booster vaccination for adult hemodialysis patients.
Known or Presumed Exposure to Hepatitis B Virus: Unprotected individuals with known or presumed exposure to the hepatitis B virus (e.g., neonates born of infected mothers, others experiencing percutaneous or permucosal exposure) should be given hepatitis B immune globulin (HBIG) in addition to ENGERIX-B in accordance with ACIP recommendations1 and with the package insert for HBIG. ENGERIX-B can be given on either dosing schedule (see above).