I think the er doc is right and your levels are okay but I personally would want my progesterone being tested. I regret that I didn't do that with my last pregnancies. Here is info on hcg doubling time quoted from here,
http://baby2see.com/preconception/hcg.html
A single hCG value doesn't give enough information about the health or viability of the pregnancy. Within the first 2 - 4 weeks after fertilization, hCG usually doubles every 48 - 72 hours. That usually corresponds to hCG levels below 1200 IU. From 1200 - 6000, the hCG usually takes 72-96 hours to double. Above 6000 IU, the hCG often takes over four days to double. So, the rate of increase in hCG levels normally varies as a pregnancy progresses. hCG that does not double every two to three days does not necessarily indicate a problem with the pregnancy. Some normal pregnancies will have quite low levels of hCG, and result in perfect babies.