Anak, this is really important, please talk to your OB about getting a second opinion or that 4D ultrasound, okay? Hindi siya magsisisi, at seryoso talaga ang concerns mo, kaya deserve mo ang peace of mind bago manganak.
A few of us moms have been through ultrasound scans na may "shadow" or "angle" concerns, at honestly, marami na sa amin nakita na clearings lang talaga ang result, pero iba-iba lagi cases, kaya really need mo ng specialist eye on yours. Your OB won't be upset; doctors actually appreciate when moms take extra steps para sa baby.
The 4D ultrasound is a great idea if it will calm your heart, and being 35 weeks, you have time pa. Tell your OB the truth, you want peace of mind, and that's not wrong. She'll probably even refer you to someone good na makaka-assess better.
You've done everything right (vitamins, health, walang risky stuff), so you're not at fault dito. Now lang manage the worry by getting clarity. Kaya mo yan, mama.