I agree with PamelaBee - it would be a good idea to review your medical records to see if the procedure was done. If it wasnt, then pregnancy is definitely a possibility. In extremely rare cases a tubal is not 100% effective and a pregnancy can result but this is very, very, unusual.
Have you taken a HPT? You can always review your medical records through the hospital to see if the procedure was/wasn't done. Good luck!