Generally one kidney is larger than the other in all humans. This is something that shouldent be worried about unless a medical physician diagnoses a kidney problem which is a results in one kidney being larger in size.
It is completely normal to have one kidney smaller than the other. Many people can lead a normal life with just one kidney. It is not clear why the human body has two kidneys. People who have one kidney smaller will need some testing to be sure that further treatment or observation is not needed.
The only problem is if the smaller one is smaller than an average sized kidney. If both kidneys are within normal size, just one is larger, this is not a problem. In fact, many people have this condition and never become aware of it.
This is actually normal, so no, you shouldn't be. There is medication that can help, but it might not be successful. People can live with just one kidney, so the fact that one is larger than the other isn't a big deal, other than the fact they will be able to hold more liquids.
I have known two mothers who have experienced this and in both cases they were told that the smaller kidney would likely catch up and not be a problem.
There is no health risk in this. The only possible exception is if one kidney is larger due to infection or cysts, which are health risks on their own.