Well done finishing this game!
Here are some thoughts that I don't see in other comments:
- you can save some time by not doing the level selection and launching the next level automatically
- pixel graphics are very tricky to work with, and unaligned scaling of different objects will end up looking a bit rough (like the chair in levels 2 and 4, or the bookshelf in levels 1 and 3 (where it is even doubled to make a wall), or all the buttons using the same background but scaled differently), this is worth exploring more
Keep it up!