Fetus kidney

Mommies, I just need to hear some stories and some comfort so plz give feedback. I went in at 19 weeks to find out gender of baby. It's a boy yay!!! Later my doctor went over the ultrasound pics with us and said ONE of his kidneys had a little extra fluid in it. She didn't say how much all she said was it was nothing at all to worry about and it usually clears up by itself. I'm supposed to go back in for another ultrasound at 32 weeks. I can't help but worry tho. I'm terrified. I'm 21. This is my first baby. A little feedback would be much appreciated!