Struggling with the school level because the paper airplane won't dissappear into the blue wall- but otherwise fun game!
For around twenty minutes, I was stuck at this stage too and had attempted it twice after restarting in the hopes of correcting some bug. The items I had left to remove were: blue paper airplane, green desk, red chair, orange desk, navy desk, pink desk, and purple book. However, I just finished the classroom after referencing Mobile Gamer Dad's video on YouTube. For some items including the purple book, they must be aligned at a specific angle for them to disappear. Hope you're able to move forward like I was able to!