Lowest centile

Susie • 24,fianceé,mama.💍👶🏼 16-11-16 Arlo 💙 13-04-18 Ezra 💙
Should I be worried? Little man is measuring on the lowest centile for 28+6 weeks,which explains why I'm not very big,however,at my 4D scan last night they estimated he weighs about 2lb 10oz.. Which is more accurate? Midwife measurements or scan measurements?