Good news! It's reading 28C right now, and that's just on the bad thermometer I've got. One of my relatives is coming over lately with the infrared gun though so I can properly read the temperatures. I've also ordered a probe thermometer as well.

I think it was a combination of two things (other than having a bad thermometer): the radiators in my house being off, and the box needing more time to heat up properly. Hopefully I will perfect the art of temperatures soon though!

I think I got confused because my thermostat probe inside the RUB is reading at 25C, in comparison to my thermometer which is measuring 28C.