How worried should I be about small measurements at 35 weeks?

I went in to see my maternal fetal specialist for a scan today and discovered that despite being 35 weeks 1 day, that my baby only weighs around 4 lbs. Additionally, my amniotic fluid is a bit low and the doctor told me it's a possibility that I may need to deliver early. My placenta and umbilical cord looked good. I'm really worried now, does anyone here have any experience with this? My doctor went through this very quickly and I didn't want to hold him up as I know he's very busy, so I have a lot of unanswered questions...