I couldn't tell if you were using a power meter. For the rest of that 3:30 ride, I was at endurance pace, so about 1400 calories for the 2:30 at endurance pace and another 800 for the hour at Z4/5 is probably how it worked out.

If it's an organized century, don't forget to eat at the rest stops, secure in the knowledge that you'll burn it off.