low HCG of 42 at 4W 3D... need reassurance:(

Hi Ladies, hoping for some reassurance. My LMP was Jan 28. I ovulated on 13 Feb. I have a history of irregular periods ever since I had major surgery 6 months ago. My last cycle was 40 days and before that I had no period for about 55 days. I found out I was pregnant with our first child on 26 Feb with a faint positive pregnancy test, I had a blood test on 1 March at 4W 3D to confirm the pregnancy. It was only 42 HCG and the nurse who phoned with my results told me the HCG was on the low side. I was very stressed to hear that and asked for the Dr to call me. The Dr called that night and told me to stop stressing. I asked if I could do another blood test in a few days, my Dr said no because it would only cause stress that's bad for the baby. She specialises in maternal care and she told me that there's nothing to worry about and every woman is different. She said she would only test again if I was bleeding or having heavy cramping. Meanwhile I took a clear blue weeks indicator test and got 2-3 weeks result which the leaflet explains is consistent with 4-5w pregnant. And all my other tests have gotten darker lines every day. Now as dark as it can get.  I carried on with my pregnancy and am now 6W exactly. My midwife has me in for an early scan at 6W 5D so next week, and I'm really terrified that I'll have miscarried with the low HCG result I had last week. I  have all the right symptoms - nausea, sore breasts, diarrhea, food aversions, extreme fatigue, light cramps every so often. I "feel" pregnant and I know time will tell with my scan in a few days, but I'm just seeking some reassurance from ladies who had low HCG early on in their pregnancies who went on to have healthy babies/good ultrasound results. Thanks so much X