GET YOUR OWN BACK means to get some kind of revenge, to do or get something in return for a bad thing someone did to you.
The director has been unfair to the teachers all week, so here’s your chance to prove you’re right and get your own back.
I hope you haven’t done anything silly just to get your own back because I went away.
Don’t worry about what people might say about you. Anyone can complain, but in the long run courtesy and patience are the best way to get your own back.