Made my first NO Go decision today.

I am currently a student pilot working on my PPL. Today I was supposed to do a local solo flight to work on take off and landings but when I was doing my run up I noticed something with the Carburetor heat. When I turned it on there was 0 drop in the Rpm or change in the engine noise. It was also noticeabley rough to pull out the nozzle. I tested it a few times and when I saw no change I decided to taxi back and squawk the airplane. I just got a email saying that it was an invalid squawk. Im currently waiting on my instructor to get back to me but im not sure why it would be an invalid squawk. I mean I know I made the right decision of not flying because I wasnt comfortable with it. Any opinions on it?

https://redd.it/1x1qcw7
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