hi lmp  is last monthly periodes first date. i see that  there  is a discrepancy of 2 weeks between your gestational  age and scan corrected age. there are 2 possiblities. either you wre wrong about dates which is very common or in this cycle your egg release was late and you concieved then. this can be confirmed further by finding interval growth is ok when we do your anomaly scan at18 to 20 weeks.