I am sure you are upset but I will add to the chorus of people telling you not to panic.
I have experience with solid organ donation -- not directly as a donor or recipient, but coordinating it. Kidneys are organs that LIVING people are able to give to unrelated others so long as tissue types match up. It used to be that kidney recipients only got them from "cadaveric" donors -- for example, people who died in car accidents -- but the need was so great and the number of donors so small that the medical community decided it was ethical to allow people to give away (not sell!) one of their kidneys. The reason this is now allowed is that studies show that people who have only one kidney statistically live just as long as people with two.
So there are real numbers backing up that seemingly nonchalant attitude. I'm sure they are just trying to make you feel better, if it comes off as cold well that's a bedside manner problem that's for another post.
I have heard of situations where people wanted to donate their kidneys after death, but when the physicians went to get them they found only one, or a single horseshoe shaped kidney...there are so many anatomical variations that are considered normal and that you'd never even know about if a surgeon didn't look.
So try not to panic. This is not nearly as bad as being told there is a heart or brain problem, and it may not really pose a problem at all...in the days before ultrasound, you might never have known and it might never have mattered.