My HCG levels are still rising dramatically, but my Dr. told me I was going to miscarry, could she be wrong?

I went in for my 8 week prenatal exam on 6/9 and they could see the sac, but they didn't see anything inside of it. My periods had been irregular before conception, so it is hard to determine the estimated date of conception. I went to the nearby hospital for a more high-tech ultrasound and they still couldn't see anything. My Dr. then recommended that I have a d&c. I asked if it was a possibility that I may not be as far along as they thought and she told me it was unlikely that the pregnancy was viable. I had my hcg levels checked on 6/9 and it was at 18,000 and then checked again on 6/11 and it had risen to 23000. I can't have a d&c with peace of mind until they are 100% sure. I am just wondering if it is possible for the pregnancy to not be viable, but still have rising HCG levels.