I used to work as a security guard in a school and I let my friends in at night so they could play basketball and swim

I was working in a school as a security guard at night and during the weekends, so I used to have the keys and the alarm codes to enter and leave. I was only 18 at the time and my friends came up to me with the idea of letting them in so that they could play basketball and my sister could swim with her friends. I was more inclined to do it because I had already done it once (and we didn't get caught) and also because my sister was going to be there, it wasn't only boys getting into the school. We did it for around 6 months and we never got caught, we always left everything as it was before, the pool was always tidy and clean after and the gym as well, so they didn't even noticed we were there. I got fired for no reason (maybe it was because I was too young to be working with that kind of responsibility) but they never really told me.