Bright spot found on my baby's heart

Hi everyone, just wanted to see if anyone had any experience with this. On my anatomy scan and level 2 ultrasound, an EIF or bright spot was found on my baby's heart (left ventricle). I am really worried because it's one of the markers for Down syndrome. Based on my age alone, I'm 31, the peritonologist said I have a 1 in 600 (but online it says it's 1 in 900) chance of having a baby with DS, but with the EIF it increase the risk two-fold, which puts me at 1 in 300. I haven't had any screening or blood tests done, even though they offered it to me. My reason for delaying to get diagnostic testing is because I am really scared to find out the results, and also because it's too late to do do anything about it if the results are negative. I think even if we found out if it had DS, I wouldn't want to get rid of our baby. My question is, what are the chances of having a baby with  DS with only one marker? Please share any information you may have because I want to stop worrying about this.