Please help

I had my last period October 10th missed it this month, got a positive pregnancy test from his hospital this past Saturday, they told me my levels were at 345. The dr said that was perfectly normal. So here I am thinking I'm fine and a happy almost 6 weeks (on Saturday according too my LMP) pregnant and my gyn calls me telling me she was going over my case, and she didn't realize how low my levels were and she just got the lab results from this hospital from Saturday. I told her the dr at the hospital said the levels were fine, and my gyn tells me they were low and there's a chance the baby didn't attach correctly and I should prepare myself for a miscarriage! I'm so heartbroken. I just had a miscarriage this last September ( I know I got pregnant fast) I'm so scared. Has anyone else had levels in the 300's around their 5th week and went on to have healthy babies? Or has anything similar happened to any of you ladies? Anything would be encouraging right now