It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle.
It was also the only stage of the Saturn stack that had a non-gimbaling engine, making it even simpler; all directional control was done by the reaction control system, which was almost as simple and, of course, had been tested on the descent.
On the other hand, IIRC it was also the only engine in the Saturn stack that couldn't be tested before launch, as the fuels were so corrosive that the engine could only be used once before needing extensive rebuilding. So lighting it was always a bit of a nail-biter; unlike every other engine in the vehicle, if it didn't work the first time, the astronauts died.