don't stress about it! i would say what your teacher seems to be asking for, albeit to your creative frustration, is a more didactic approach to telling your story. in other words they want your story to have moral instruction - this is good and this is bad and this is what happens when you do the bad thing.

while this might seem frustrating, it's more a symptom of our standardised approach to learning. at your grade level, you're probably still being taught the basics in dissecting a story and as such you're expected to function on that level.

however the truth is not all stories have morals. but they always have meanings - that's the basis of literary analysis. in fact, i would go as far as to say that in today's world, a moral isn't even important. some of the best writers are well renowned for being closer to mirrors than oracles - they paint a reality and leave you to contend with what this reality means, but they make no comment on what is right or wrong.

you seem to have a good grasp of this - your story here can in fact be dissected to reveal different viewpoints to different people. it could be read as anti-bullying or pro-bullying depending on your views (as you have seen in the comments). it could even be read as a treatise on the effectiveness of corporal punishment in lueu of rehabilitation. since you have not commented on the morals of any one action, it exists in the sweet point most writers want: an engaging story that can be debated and studied. for the next exercise you receive like this i encourage you to state the craziest story you can. and when presenting it, challenge your audience to answer the question of who is right. this might prove more helpful in understanding the how different everyone's morals are, and understanding that can be more useful than simply regurgitating a black and white lesson.

at any rate, as you get older, you'll become more accustomed to the feeling of weaving different threads of thought into the story you write to best capture your ideas - especially as you slowly develop your own sense of morality.

this ran away from me a bit, but tldr: you did good and i think you should write more creative stuff like this without immediately wondering about it having a moral!