Should i be concerned? Spot on baby's heart.

6 weeks ago at my first ultra-sound, the doctor told me there was a calcium build-up on my little girl's heart. I think she said it was called 'Echogenic Focus'. She basically told me that it was a muscle on the heart that was glowing. Then she told me that it was also a soft-marker for down-syndrome. :( All of my test came back negative for down-syndrome, but she still told me that there is a chance that my little one could still be born with it. So after crying and worrying, i went to see my ob/gyn and he told me that it was nothing to worry about and that it should go away by the time i had my next ultra-sound. After hearing that i stopped worrying. Well, this past Thursday i had the other ultra-sound, expecting everything to be fine with my baby. Turns out, the spot was still there and the only thing the ultra-sound doctor told me was "well, we'll see when the baby is born." Are you serious?? Should i be concerned? i've done nothing but cry and worry since the ultra-sound. Is there anything i should be doing that i'm not? or is there something i shouldn't be doing? Down-syndrome doesn't run in my family or my fiance's so i don't understand how is could be possible for my little girl to be born with it. The doctor said that 4-7% of healthy babies are born with echogenic focus, does that mean that there is a 90-something % chance my baby could have down-syndrome? The doctor really didn't give me much of an answer, so any kind of insight would be GREATLY appreciated. I'm worred sick :(