I also noticed that the pixel art asset you used are blurry, and they shouldn't be.
So in Unity, when you import an image file, the game engine will give it a filter by default, which makes pixel arts blurry (pretty stupid, i know). To fix it is very simple. You just gotta select the image and look at the inspector panel and there should be the filter options as part of the import settings. Remember to click apply when you are done.