I had a blood draw on CD29 with one of my pregnancies and according to the doctor it came back negative. Two weeks later still no AF so I tested at home and got a blazingly bright BFP. DS will be 4 next month. With my current bubs, my hCG was 38 at 13dpo and 236 4 days later. The dr said, "I'm sorry but you are going to miscarry." I said, "Uh okay. Bye." and promptly switched doctors. I'm now 11+3 with that same bubs that the first doctor said I'd lose before 9 weeks.
As someone else pointed out, that number has to rise from 0 and you had your blood draw done VERY early. I wouldn't worry at this point. It not what the number is but how fast it rises. With DS, my hCG was only around 12000 at 6 weeks and 17000 at 7 weeks yet I still made it to full-term.