Measuring small

I am currently 30 weeks pregnant and measuring 27cm for fundus height.  They did an ultrasound and she is 3.1lbs, but the unltrasound tech said she is at the 20th percentile in overall size.  Everything I have read online says that the average weight of a baby at 30 weeks is 3 lbs so why are they saying she is only in the 20th percentile.  I have gained plenty of weight so far at 21lbs so I know its not that I am not feeding her enough. Should I be concerned?
Also she is currently breach.  What are the chances she will turn on her own in time for labor?
Thanks for your feedback.

[JoyRenee]

Well if she is breech then that is most likely what is affecting your fundal height measurements. I would NOT read into those measurements closely, especially if a sonogram showed your baby to be perfectly normal and healthy. They can be off for a variety of reasons and most doctors don't take them seriously anyway, especially in the late 3rd trimester.