I don't have a lot of experience with this, but I've heard at least a few stories of very slow rising HcG levels and the pregnancies being totally fine. If your doctor isn't concerned, I would try to relax and see how things look on the u/s tomorrow, though I know how difficult that would be.
Beautiful baby girl born 8/13/2012. Little star baby lost at 10 weeks pregnant, 12/18/2013. Rainbow baby girl born 12/22/2014.