Soft marker

Okay so we got our anatomy ultrasound a few weeks ago and doctor called last week saying that they wanted more pictures and they essentially didn't get good enough pictures of heart, spine, and brain. (Glad I spent $60 on that ultrasound lol) so I've been waiting on the call to do a second ultrasound and yesterday when I saw my doctor she said that in the first ultrasound there was a bright spot on the babies heart and she said that it's pretty normal and really not anything to worry about, but it was a soft marker for Down syndrome. There are no other signs at this point that that's what it would be. She said it could have been a bad picture or a calcium deposit. Has anyone else heard of this before? She told me not to worry but how can I not?