I have to say that I am using 3.3V not 5V cause I found after a little search that gives more accurate temperature.
Then those numbers you are seeing must be accurate.
The reason for using 5V is because the values read from the sensor are on a scale of 0 to 1023, where 0 corresponds to 0 volts, and 1023 corresponds to 5V.
You are using an incorrect mapping from reading to voltage when you use 3.3 on a 5V system.