I assume you checked your coolant level right? If the coolant is at the proper level you may have air in the system. There should be a bleeder valve for the cooling system on or near the upper radiator hose connection into the thermostat housing. With the engine fully warmed up and the heater turned up full, open the bleeder valve with a 12 MM wrench until coolant comes out. You will probably see tons of little bubbles. (If you have trouble getting the coolant/air bubbles to come out of the bleeder, just rev the engine a bit, should shoot right out.) Repeat this step a few times until you no longer see air bubbles. It should only be a steady stream of clean coolant. Tighten the bleeder valve, and take the car for a ride to make sure it stays at normal operating temp, be sure there is no leaks, and also that the fan is kicking on.
If the coolant level is ok and you cannot not find a bleeder valve near the upper radiator hose or thermostat then the way to do it is the old fashioned way I always use. With a cold engine, remove the radiator cap and run the engine until the gauge registers normal operating temprature. Then turn the heater control to full heat. You should see the coolant level drop through the cap opening. Have your coolant ready and add till it is full. Let the engine run to see if the level drops a bit more. Once it stops dropping, replace the cap and turn the engine off.