The only advice I would like to give in terms of writing this story or indeed writing anything is to just keep at it. There are always going to problems with your first go of anything, and that’s natural because nobody creates a perfect piece of writing on the first attempt. Although with writing a proper book or story the best thing to do is get a thesaurus. In fact, a thesaurus will become your best friend, It’s not really cheating either as that’s what they are there for.
But I think it’s also important to just focus on telling the story, because a lot of people tend to spend so long describing something or setting a scene that it can be quite off putting to the person reading it, unless they have a very high tolerance for knowing exactly how something looks 
Another suggestion although it seems silly to mention it is that you have to read a lot more. The way I’ve just said that sounds insulting, but i honestly didn’t mean it like that. People who want to write have to read and read and keep it up, because it’s the best way to learn.
Ultimately though, you just have to focus on telling your story and making sure that you are happy with it. After all, you’re not writing this for anyone else but yourself. Sure, you would like people to read it and enjoy it. But you have to remember that this is your story, and as long as you have a reason for everything that happens in your writing then nobody can fault it.
All writers have their own rules that they try and stick to and abide by, which is why you well never get definitive advice from anyone. Apart from the old saying that practice is perfect, you’ve just gotta keep at it and be your own hardest critic. It’s helpful to see your own flaws in your work so that you won’t get offended when people point them out, and in doing so you can sometimes manage to fix whatever problems you initially had with the story before anyone else gets to see it.
I mean, you’ve got a bit of work to do and perhaps you should maybe set the scene a little bit more. For instance, you could tell the read what the location looks like and go into detail about how the creature looks, but just remember to keep having fun whilst writing. If you’re passionate enough about what you’re putting onto the page then it will shine through in the work, so just keep at it and i’m sure you’ll produce a great story as an end result! 
Hopefully that was of some help to you.