So I just had a quick skim through your creative and your language seems to be very advanced and formal, well done on that. However try not to overdo it with the academic language because sometimes sentences can lose their meaning if they're too overpacked and enhanced. Sometimes keeping it simple has a bigger impact. Also it is very important that you kept your story to a brief, short moment and didn't extend it over a longer period.
However I think you lost marks because the discovery in it isn't crystal clear; I can see where you're coming from, but try to make the discovery stand out more. Depending on the stimulus of the exam, it might be even harder to adjust it, but ensure that your story has a clear and straightforward sense of discovery in it (I cannot stress this enough

). I got a 13/15 for my half yearly because my story didn't
explicitly demonstrate discovery. I was so upset because my language, format and setting were near perfect. I was so proud of it and it was very demotivating to get back a mark like that.
I know, it's stupid and frustrating, because we as writers can clearly see the deep and intellectual discovery behind our stories and it isn't really our fault that the marker doesn't get it even though it is assumed they should since they're HSC markers/ teachers. I hope this helped!