Congrats on the chicks!
Don't need to fuss too much with temp and adjustments. If the thermostat is working right and placed in a neutral area which it should be on a commercial model, adding heat inside via candle or hand warmer shouldn't affect the incubator over all temp. However, if your thermometer probe was near a hot egg with a fiesty chick, that can explain why the thermometer is reading high, and now if the probe is not near a hot chick, and you touched the thermostat to adjust for hot chick measurement, that is probably why it is reading low. Calibrate with the bator empty, and providing air flow isn't horibly disrupted by the addition of eggs, the temps should be fine.