I had really low HCG levels after my first bloodtest at just over 4 weeks. It was around the 60 mark for memory. I had to return for another blood test to make sure they were rising (roughly doubling every couple of days) and they were so all was good. I have a very healthy 10 month old DD now so the low levels meant nothing in my case

Try not to stress. Low levels are very common and while it's good to prepare for the worst in some cases, I'd say enjoy the moment and stay positive. Good luck!