What should I do if I made a mistake at work and am afraid of getting fired?

I work as a night auditor at a hotel, working overnights. I had brought a bag of popcorn for my dinner one night and popped it in the employee break room. The microwave in there is not the best. The popcorn burned as I was in the hallway to check on it (in there for less than 2 minutes). This set off the alarm which tiggers the fire department. I was trying to silence the alarm while answering the phone letting guests know that it was a false alarm. The regional manager was staying at the hotel, and she came down. The fire department came after I’d already reset the alarm—which is a no-no apparently. I’m now scared that because it was my fault that there was a false alarm that I’ll get fired. I tried to handle it as best as possible, but guests were complaining about the alarm and I couldn’t figure out how to silence it. Would this be a reasoning to fire someone? With how it is now, I would not be able to find a job, at least not with enough pay.