Hey there! :3

So firstly, your terrain. It works - you have variety in the levels and a nice river running through the middle to add diversity and colour. You could mix in some other block types with the grass to add some more detail, like coloured clay or some gravel paths leading to various places. I do like the wheat on the hill, however, and the reeds along the coast - these are nice additions of detail ^.^

Secondly, your organics. You have them placed well on your plot, but they're spawned. Spawned trees are instantly rejected because they lack creativity and are too easy. If you struggle building trees, I recommend you search 'Plutouthere' on YouTube and check out his tutorials :3

Lastly, your structure. I understand the idea behind it, but unfortunately it just doesn't show enough detailing to pass. If the rest of your plot was amazing, it'd be accepted. But because the rest is fairly simplistic, I'm afraid the building is going to need to be better. I'm a huge fan of Harry Potter, and I like the idea you were going for, it is really creative. But the structure lacks detail and depth, which are two fundamental parts to a building. I think the use of logs on it is really nice, however, but the palette is also pretty simple - you only have two main block types.
It may be helpful to add a frame.
Simple frame:  https://imgur.com/ONsoRxh
More complex frame: https://imgur.com/20eZjP8
There's just an idea of a frame, both fairly simple still, but helpful hopefully. It just adds that little bit of depth and is extremely helpful to apply detail.

I do, however, really like the bridge. It's a little bigger than it really needs to be, but it has nice depth and attention to detail, and I like how you've used the slabs to add levels in the middle of it :p

Good luck!
- Dutty :3