Advice and encouragement WELCOME!

I'm a serious worrier. I know it won't help anything but it's in my DNA. SO, at my 19 week ultrasound to determine sex and get regular measurements of the baby, we found out that we're having a girl (yay!! 2nd girl!!) and we also found out at my follow up OB appt that one of the baby's kidneys was slightly dilated (enlarged). It was slight but I was advised to have a follow up ultrasound in 3-4 weeks, which happened today. I am 6 months pregnant today. Baby is growing great and is right on target. They were able to get some good photos that they couldn't get the first time because of her position but today was better. Good brain photos, heart photos, diaphraghm photos, etc. But, when they mentioned that the enlarged kidney (still slightly dilated) could be an indicator of Downs Syndrome, I panicked. NOT because I'm bothered by it at all. But because I'm worried about my baby's health, etc. I just want it all to be ok. BUT, she did say that she didn't see anything else that would alert them....so I guess it'd be a soft indicator- no hard evidence to show that downs syndrome is the outcome. I cannot do amniocentesis because I'm too far along and it can cause miscarriage- plus, I didn't want to do it at all early in my pregnancy. But, I was told that I can do a blood test that is not harmful to myself or the fetus. I feel guilty for wanting to know. But it won't change anything, so why do it? I'm confused.
I'd love some advice from anyone who has experienced any of this and was curious if it's something that will resolve itself. I freaked out this morning but I've come around and calm down. I love to hear from ALL of you and would appreciate the encouragement.
Thank you in advance.

Re: Baby's kidney is dilated in ultrasound
Me: 30 dx w/PCOS 7/13
DH: 31
TTC 11/12
started Metformin 9/13
HSG, tubes open but narrow uterus... f/u with RE 3d u/s everything 'normal'
2/14: hopefully 1st IUI... timing off before trip, waiting until 4/14
3/27: POAS= BFP!!!
3/28: beta#1: 108
4/2: beta#2: 799
4/11: u/s 6w1d EDD 12/4, 1 little penguin!
7/7: We're having a girl!
12/11: after lots of labor/delivery/nicu excitment baby Piper Mae born 1859 @ 8lbs, 21.5"
Samuel Jacob
Due 2/16/17