The following is a quote from the wikipedia article about the Apollo 11 mission
Apollo 11 entered a near-circular Earth orbit at an altitude of 100.4
nautical miles (185.9 km) by 98.9 nautical miles (183.2 km), twelve
minutes into its flight.
It appears that orbit description in the form of 'X by Y' refers to near-circular orbit.
I gather from the wikipedia article that the first burn of the third stage completed insertion in a very low Earth orbit. I assume that if for any reason the mission would have to be aborted at that point in time the orbit would give the astronauts time to prepare for re-entry.
I assume that after checks were completed the go ahead was given for the second burn of the third stage, to bring the spacecraft on a trajectory to the Moon.
Once the spacecraft is on its trajectory to the Moon there is no turning back. The only way back to Earth is by going around the Moon. The trajectory to the Moon was calculated in such a way that the gravity of the Moon would swing the spacecraft around the Moon and back on course to Earth, with no need for a main engine burn, only course corrections by firing smaller thrusters.