If the heater is blowing hot air, you likely have nothing to worry about. Temperature gauges vary from one vehicle to the next. They also tend to read lower in cold weather because radiators are so efficient at removing heat. If you're in doubt, have your mechanic connect a scanner that displays live data. It will show the exact coolant temperature based on a different sensor, not the one for the gauge.
I have the same condition on my '88 Grand Caravan. Just got home an hour ago. It's 15 degrees outside and the temperature gauge was reading less than 1/4 scale, but the heater is working just fine. In summer the gauge reads about 3/8 scale.