Step-by-step explanation:
start with an introduction explaining how your school is holding a music competition, then include in the thesis statement that some thing went well some could be improved
in the the body paragraph write about the good part of the music competition and expand a bit your idea( detail it a little, not too much otherwise your word limit will be crossed by a lot)
then about the part that could be improved in that competition
conclude it by saying it was good overall and you hope next year it goes better or more as planned