Hcg at 7 weeks 2 days

So i cant my ultrasound until saturday (ill be 11 wks 3 days). At 7 weeks and 2 days i had my blood test and hcg was 27,000. Went back to the doctor, confirmed the pregnancy and put me onto an obgyn. Last week when I went to the Obgyn and he read my results he said 'we will have to keep an eye on that' but wouldnt tell me what was wrong and just kept saying it was nothing. I feel like 27,000 is on the lower end of the spectrum for 7 weeks. Anyone know why he might have reacted like that and if those levels are normal? Its been killing me not knowing if everythings ok.