Hay nako, I totally get your worry! So honestly, mas reliable talaga ang first ultrasound (yung transV) for dating purposes kasi yan ang most accurate way to establish your EDD, especially if it's done in the first trimester, the 3D ultrasound later on can have a wider margin of error for dating. I'd definitely bring up with your new OB on Saturday na may discrepancy between the two dates, and let her check kung saan talaga dapat based on your baby's measurements now; a few of us moms have dealt with this kasi OBs use different dating methods so best to get clarity straight from her. Don't worry too much, ang important ay healthy ka and baby, but it's good na alam mo exactly kung kailan ang expected delivery!