Ay mama, I totally get the confusion kasi ang dating confusing talaga ng dating! Based sa most cases na narinig ko from my mum friends, ang ultrasound ay usually mas accurate lalo na kung done early sa pregnancy (first trimester), kaya kung April 10 ang EDD mo based sa last ultrasound mo, that's probably your more reliable date, pero honestly, since medyo may discrepancy kayo, best talaga na i-ask directly sa OB mo on March 15 para sure, especially since second baby mo na rin and baka may factors na need i-consider. With your first baby, baka different circumstances din kung bakit nag-deliver ka earlier, so don't stress too much, babies come when they're ready! Anyway, wag nang mag-overthink masyado, the important thing is you're almost there na, mama!