With the Intel® Core™ i3-2120 80c would be high under load. I would expect to see temperatures in the 60s with the stock cooler.
I would guess that you just build this and the stock HSF (heatsink/fan) isnt seated well. To test this reach in and see if you can pull any of the twist clips straight up. If you can pull any of them then the HSF was seated well and you are going to want to reseat it.
If this isnt the case check the program that you are getting the temperature reading from with another to check to make sure they match up.