I have set the Mini Mat temperature to 70°C for 3 hours and have covered it with a thick blanket as you recommend, but I am noticing that the temperature has increased to 72°C on its own. It also fluctuates between 50 and 70°C, is this normal function?

If it is the first time you use the mat, it may be better to let it air out without covering it.

It is normal for the temperature to fluctuate slightly when the mat/belt is in the same state.
A difference of +/- 10°C, when the mat is in the same state, is fine. 

It works so that the heating area of the mat warms up to a little higher level and then stops to allow the temperature to go down. 

When the mat cools to 5-10°C lower than the set level, it resumes again to achieve a little higher than the set level and so on. This is a standard function of thermostat-type devices.

If you change the state of the mat’s thermal insulation, for example, if you stand up from the mat or remove the blanket and protector and let it sit uncovered for 5 minutes, the temperature may drop 20°C because the hot crystals’ heat will dissipate quickly. 

They will get warm to the touch, and even though the temperature indicated on the controller will go up to 65°C again, the mat will be only warm to touch unless you cover or lay on it again.