Wonderful^^
I do recommend you to have a chart ready. A chart is like a plot board for you to understand and extend your story. Also, do take note of which chapter you will end the fanfic. Take, for example, chapter 30 is where it ends, chapter 10 is where the characters get together and etc. To add, describe what's happening to each character, take for example:
Melissa pondered over the change that was happening to the world. It was changing rapidly that even she can not comprehend what was happening. Emotions were stirring inside of her. Her home. Her beloved home was being destroyed by the cataclysmic power. "N_No... How can this be... This wasn't meant to happen!" (It sounds cringe lol.)
Oh and also Grammar, capitalization, punctuation, and spelling are important, so use Grammarly. If you don't have it, just make sure in every sentence that you think needs a comma, please do add^^
But in total, you are already doing great!^^