220v to 110v outlet

I am changing my electric stove to a gas stove top that will only require a 110v outlet. I hired someone that did the work however not sure if he did it properly. I currently have a double throw 30 amp breaker and it was my understanding that you should have replaced that with a single 15 amp. I questioned the work and was told the wires match. A 30 amp breaker is required to have number 10 wire I just figure there's no reason to change the breaker it's just a 30 amp single pole circuit on a 110-volt circuit Outlet so there's no danger. He stated he capped off one wire by the outlet.