I went to an RE who counted an HCG of 7 or higher as pregnant.
If you look in my bio for this PG my first HCG was 12, second was 31, so I had a late implanter but my numbers doubled appropriately. Did your Dr. schedule you a follow up blood draw to see if your numbers rise?
I am almost 13 weeks PG and for what it's worth, I was getting negative HPT with the HCG level of 12.
GL,
JM