I have always wondered if they had more in case they needed them.
On August 10th, 1945 the U.S. had exactly as many atomic bombs as any other country in the world. The U.S. had the capacity of producing approximately one nuclear weapon per month and fully intended using them Target number three was Tokyo.
The U.S. actually drew up schedules and was making target lists. Ironically, Hiroshima had been largely spared conventional bombing because the U.S. wanted to keep it “pristine” to evaluate the effect of atomic bombs. The locals believed they had been spared because many people from the Hiroshima area had emigrated to the United States during the late 19th and early 20th Centuries.