Downs Syndrome?

Victoria

I had an ultrasound done at 20 weeks, 5 days. The doctor inspected pretty quickly. He said he saw two spots in the stomach (after research i have seen it called “double bubble”) and said it was Down Syndrome. However, when I started researching it after the appt, there’s 7-8 other markers to look for in a baby in an ultrasound. Shouldn’t he have checked those to maybe confirm that and not just the stomach? Has this happened to anyone else?