When our son was a month old we did a Pidyon HaBen. Many years later we discovered that my wife is a bas levy and therefore we didn’t need to do a Pidyon HaBen. Do we need to ask Mr Cohen for a refund?! (In practice he gave us a coin we then used to buy our son, so we we didn’t actually pay any money – but we’d like to know if there is any consequence of doing this mitzvah we didn’t need to do).
The fact that you did the pidyon when you didn’t have to doesn’t have any consequences, except for the fact that there was a bracha l’vatala made.