Don't up the temp on the thermostat, just trust the Herpstat temp and try not to worry too much. Accurites (in spite of what the name might lead you to believe) are not the most accurate. It's not uncommon for them to be off by 3 degrees or more. Even the probe and temp. sensor in the unit are often by several tenths if not more.

Just make sure that the Herpstat probe is close to the egg box (on the outside) to give an accurate reading of the incubator air temp.