3D ultrasound sex reveal

So I just had a doc appt 2 days ago & I thought we might find out the sex because I'm almost 15 weeks. My doc didn't check, she just did a quick look to see the baby was healthy & that was it. I'm happy my baby is healthy but the suspense of not knowing what I'm having is driving me crazy! How accurate is going to get a 3D ultrasound to determine the sex? Any experiences? Won't find out with my doc until 20 weeks. I can't wait that long!!!!