Baby girl measuring really small

I am 37 weeks today. I went to the doctor on Monday and my little girl is head down. Which is great but the doctor is still saying she is really small. He doesn't seem concerned that she is tiny because I was 103lbs before pregnancy. But I figured at 37 weeks she would be at least 6lbs. He said she is closer to 4.5-5lbs and I should expect her to arrive in 2-3 weeks. He also said by then she would be about 6.5-7lbs. Should I be concerned that she is still so tiny?