Low PAPP-a and scared!!!!

I was told that bloodwork taken at 11 weeks 6 days showed a Papp-a of .35 and that put me in the 1st percentile. The doctor briefly went over it and said I would need extra ultrasounds and it could possibly lead to low birth weight or preterm labor. I never heard of it so naturally I googled..... ohhhhhh boy! I was hysterically crying. I called the office for a better understanding.

I asked what my numbers were- .35

I asked what it was with my first born- 5th percentile (she was full term 8lbs)

Doctor keeps telling me I shouldn’t worry... but now that’s all I can do. Someone give me a positive story! Please!