Confused... Need to repeat anatomy scan.

So I had my anatomy scan on Monday and it went well but I got called that I need to repeat it in 2 to 4 weeks because they couldn't see a few things - 3 items that had to do with the heart. 4 chambers, and two other items. But here's the thing... Last Wednesday we had a fetal echocardiogram because my last baby had a VSD. The fetal echo checked out perfectly - no issues. I'm just so confused.... Of course I'll go and look at my baby again! I got to see my last baby a lot due to her issues, but the unnecessary concern is stressful.