Self-heating on an RTD

I assume that you have a RTD PT100

It has a resistance of 100 Ohm @ 0°C

Are you going to measure the resistance with a 50mA source?

50mA² X 100 Ohm = 0.25 W

Now you have to find out what the thermal conductivity is for the type of PT100 you plan to use. (How well is the PT100 sensing element connected to it's casing and the casing to the outside world.)

The rest of your info is a bit blurry

(0.3 mach : do you mean that your speed is 30% of the speed of sound?)

The time response in air at 62%: ??

When your air speed is that high, the effect of the airflow has to be evaluated. The air flow could heat up or cool down your probe.

But first try to get the current through the sensor down: it is to high.