I have to come in for pt 2 of the anatomy scan

So yesterday I had my anatomy scan at 20 weeks. The dr and tech said I have to come back in for a second scan in 4-6 weeks because they couldn’t get a good look at the heart or facial features, but they reassured me that what they could see everything looked fine and normal. Our little one was pretty active and not cooperating as it took the tech 4 extra times to find the gender. I guess I’m a little concerned because the tech did see the heart because he told us and I eve saw him change the ultrasound to blue and red when he was looking at it. Has anyone experienced this before?