Try not to worry, having a SUA can be normal as long as the rest of the anatomy scan was normal as well. The small growth can be due to the SUA alone.
My LO that I lost had a SUA AND cyst in the brain.....two soft markers for Trisomy 18. But we had BOTH issues. I don't want to scare you but one thing that helped me was to remember....."today I am pregnant, and I love my baby". I would tell my baby EVERY DAY, I love you and you are very very special to me."
There is nothing you can do at this point, so try not to stress, take a deep breath and enjoy being pregnant today. I'm sure all will be OK. I just was one of the unlucky 1/10000.