Hey there!

Firstly, your terrain. I get the premise, but it's way too simple. Your terrain is completely flat on all three sides - the floor, the walls and the ceiling. It's going to need some diversity in layers, not all flat, similar to what you started in the corner. I think this plot would also benefit from a mixture of blocks in the palette, not all netherrack.

Secondly, organics. The organics you've made are spawned in mushrooms. If you want to do this, please build your own. Spawned in things show no creativity and are therefore instantly rejected.

Lastly, your structure. You have none. A plot can get away with having no structure, but everything else needs to be fantastic, which unfortunately this plot isn't. It's good, but it's just a little too simple to pass.
A Nether themed building could fit nicely if you took out the ceiling. You could have a nice tall building made from netherbrick, which some coloured clay, red and oranges maybe :3

Good luck!
- Dutty :3