21 week ultrasound

I had my 21 week ultrasound yesterday and the tech took a bunch of extra picture. I went in for my appointment following and the doctor sat down and told me and my husband that baby looks great and healthy, however, there's a spot on the brain that is a soft marker for DS. I only have the one marker, never did genetic testing because it doesn't matter. I go in for a follow-up US in 3 weeks and he said he's not worried at all and it will more than likely be gone at that point. If not we'll do another US at 28 weeks. Regardless of the outcome, I love this little girl no matter what. What I'm anxious about the what ifs. Has anyone else been through this? I just need some support. I tried talking to my husband but he said he's not worried and just isn't going to think about it.