Echogeneric heart focus... Bright spot

Well i had my 20wk ultra sound then went to the doctors today, and they told me they found a eif on my baby girls heart which could be a soft marker for downs, my quad screen was negative, like 1 in 10,000 chance of downs, and my doctor told me there would have been other markers in order to really be concerned, and to not freak out because it was the only abnormality and it's very common, please tell me your experience and help me better understand