Please help

I just got out of my fetal medicine appointment to have the babies tested for Down syndrome and what not. I am 12.3 weeks pregnant and when they were looking at baby a there was a dark spot down near the belly and wants me to come back again tomorrow to see the doc. She said if it's a girl it could be ovaries or a cyst but she really didn't have answers. It was def on the lower part of the baby has anyone every had this or know anything. I'm just so worried