After replacing the Injectors car now has a cylinder three misfire

Just changed out all the injectors on my son's car because number 1 injector was bad. After I was done test drove the car, it was hard to start but after it started it ran like a dream, no misses and plenty of power. Parked the car and 2 hours later my son couldn't get it started. I checked after I got it started and now the number 3 cylinder is misfiring, and it is not the coil. Could it have been a bad new injector our was there something I needed to do after installation