The level of this description is great! this is really emotive and involves the senses really well, very engaging.
But can't help but notice that there is very little description on the fireworks themselves. I think you've captured the scene really well, short and more complex sentences work well.
Perhaps you could incorporate fireworks themselves more, it will extend your writing and maybe give you the opportunity to sculpt your writing a little more- perhaps consider short and long paragraphs and juxtaposition imagery, eg. the bright flares within the blackboard sky. etc just some ideas (I got an a* in my coursework)