Fanfiction really is a good way to practice writing. I began by trying to write a CT novelization. I got to page 10 or so, and decided that it would be better if I could make use of my own ideas more, and so decided to write a CT fanfiction instead. This was for the best for me, since my style would have been somewhat incompatable with that of true CT, I think, but nonetheless, it served as a good starting point. As I said, it lead me to my CT fanfiction, which ended being some 350 pages long, and through it I was able to practice my hand at writing and finding my style, to the point where now I am trying to write my own things (though that is a measure harder, I have found.) But be that as it may, I would say just try whatever works, as no-one is compelling you to finish it, it will serve at the very least as practice, or so I have found. Little writing ever goes to waste, after all, and even long months and years later you may find some space of wording in your earlier things that is laudable and work it into other writing.