Bright spot on ❤ or EIF

I went in to my OB for my 20 week anatomy scan to a specialist. (Although I'm only 18 weeks my doctor said I can do it early). The sonographer noticed a bright spot on my babies heart which is a soft marker for Down syndrome. I am 33 and in perfect health. So far, no issues with baby except for this. All my quad screenings & tests have come back negative for DS. Any other moms experienced this? They told me not to worry, but how could I not?! Any input is appreciated. Thanks!