What's the nominal value of your thermistor? A 10k nominal (at 25°C) would be more like 11k at 23°C.
Indeed at your target temperature a 10k nominal thermistor would be around 30k, trying to match that value for better accuracy.
Thermistors can be really accurate but you have to know the resistance of it and its pull-up resistor accurately. For that reason I prefer to use thermistors with tolerance of 1% or better and a resistor of 1% or better tolerance. Then you have just +/-0.2°C error or so.