Ay, don't worry mama, nangyari na rin yan sa ilan sa amin! The thing is, ang dating ng baby based sa first ultrasound is usually more accurate kaya yun ang gagamitin ng OB mo as your actual due date, ang second ultrasound estimate tends to be less precise na because baby's growth rate varies talaga. Best thing is just ask your doctor sa next visit to clarify kung which date siya gagamitin officially para sure kayo both, pero hindi ka naman gumawa ng mali, normal lang yan!