I'm going by my memory so I apologize if I'm confusing this bombing run with another.
...and because there was only enough fuel to make it to Tokyo but not a return flight.
They were planning on launching from the Hornet at a location closer to Japan. They planned on having enough fuel to hit Japan and fly to landing fields in unoccupied China. However a Japanese fishing boat spotted the American ships and radioed their location to Japan. The Doolittle raiders decided to launch without enough fuel to make it to China. They never considered cancelling the raid. They took off expecting to run out of fuel over Japan. Fortunately, they encountered tail winds after they dropped their bombs and most of them made it to Japanese occupied China.
I have also read that the Doolittle raid really shook up the Japanese. One B25 flew right over the Imperial Palace. Tojo was flying in a Japanese airplane and he saw the B25’s fly past him. The Japanese then pushed up their timetable for the Midway operation and went to Midway with a smaller force. The rest is history.