Ai, yes lah banyak of us kena macam ni! Masa awal pregnancy memang dating by last period je, then scan usually changes things sikit depending on baby's growth lah. Honestly tu normal je, jangan stress, some babies just measure bigger or smaller than the dates suggest, so the doc is being smart to confirm with another scan. One of my mum friends went through exact same thing and by the second scan it got sorted out, so just go with the flow and do that follow-up scan ye, pastu boleh lah settle the actual due date!