If the little plastic tab that holds the safety clip was removed, AND the pull pin was removed, and the extinguisher landed on it's handle....THEN, I could see a short spray come from it. How it blasted all over the gym....no idea. OP, did you mean to type "I finished my crunches and then blasted everyone in the gym who wasn't working out with a fire extinguisher, and then pulled the fire alarm just for lulz"??
But in all seriousness, OP, I'd just go back to the gym! So what if people look at you like you're the guy who made a mess everywhere. You are! Don't sweat it, shit happens.