Someone else has answered your immediate problem with the "regulator" issue. I'd like to address the use of propel.
I agree that you will soon discover the disadvantages of Propel as a substitute for a compressor. But you may not have the money for a compressor right now. You do not need to give up modeling just because you can't afford the compressor. Use the propel and learn a lot about airbrushing.
Airbrushing takes a lot of practice and experience to learn. You won't be getting the worlds best finishes, as a new airbrush user, even if you had a compressor. As you gain experience, the compressor becomes more desireable. I used an airbrush with Propel for over a year before I got a compressor.
BTW, a recommendation on a compressor. I recently bought an Iwata quiet compressor. At a club meeting recently the topic was tools, and one guy brought in a compressor he had recently purchased from Harbor Freight for 70 bucks. It was as quiet as my Iwata compressor that I paid twice that for! People had been extolling that harbor freight unit, but messages could not convey the actual quietness. I was impressed!