Yes, it is supposed to be smack dab in the middle.
What was the ratio of coolant to water? I find that 50/50 is way too thick... try 70 water/30 coolant ratio... Just drain some out and simply add water.
Thermostat is faulty only when you see tremendous termperature change... such as when on highway... engine is too cool... come to stop and the temp will surge high.
Fan clutch is a good possibility... easiest way to tell is normal driving over 25 MPH and temperature is normal... and when come to stop or 25MPH or lower speed.... temperature spiking higher. Another easy way to tell is pop hood open and let the engine idle on your driveway... when temp is up there and you feel the fan blowing hard, then it is working.
One other possibility is clogged fins of radiator due to bugs... simply use air hose or water and flush it out toward the front of the car from the engine bay compartment.
So if fan is working and so is the thermostat, then it has to be the coolant mixture. I find engine runs much cooler when more water is added (diluting effect).