I wouldnt worry too much, if your midwife has any concerns she would let you know. When i was pregnant DS was measuring 14 weeks at my 12 wk scan, he was growing fine then at 35 wk i was only 32 cms, but he was moving around fine so no one was too worried.
My LO came out a healthy weight of 7lb8 and now 5 months later he's only gained a couple of pound.. hes classed as 'underweight' on the charts but he's a perfect chubby little boy. So its not always best to take what the charts say is 'normal' every baby is different
Good luck with the rest of your pregnancy!
A xxx