LOL
McDonald's can't take your guns for not making the order correctly.
In fact, I'll tell you a story from when I was your age.
I worked at publix (grocery store chain in FL) and in my last months there I was a senior in HS, had the hottest girl in school, and I was headed to college on a full scholarship with money left over in my pocket in 2 weeks. I knew just how temporary that job was, so I just stopped giving a damn. The managers were adult punks. So I stopped cleaning the bathrooms, I rarely pushed in carts, and I stopped shaving for work. This pissed them off and eventually I got written up. They told me to go home and shave. I signed the writeup, gave it back, and said "I'm out of here, I don't need this." And I left. To this day, I've never needed to use them as a reference.
Now that I'm out of college and working a job that actually covers expenses and leaves some to be put away, I laugh about that job. Those "ticked off" managers are still whining about who did or didn't refill the paper towels. I make more than both of them combined. They're big fish, but in a small bowl. All they have domain over are those poor high school kids who are trying to make a few bucks and take the prom queen out to the movies. They're the people who change the work schedule so you miss work unknowingly so they can write you up and not give you a 10 cent raise. They're the people who send you into the restroom to clean turds off the floor with a single ply paper towel and laugh about it to the assistant. Like I said. Punks.
Bottom line: they have nothing on you and you can go on to better things. What they put on you does not follow you like a criminal record.