I really love the orchestral sound to this piece, it has a very strong atmosphere to it (as it should)! Overall I would say this is very solid, it has nice instrumentation and fits the boss battle theme well.
Reading your description though, I am not sure it really captures the specific vibes of what you are going for. When I listen to the song, I don't really get a sense that the character is being attacked by a disturbing creature. I feel like if you want more of that, maybe you want to go more chromatic? I'm not really sure.
Either way, great job, keep it up!