Cool concept and great execution. And awesome atmosphere!
Maybe some indication of how much and where I can expand borders could be useful since on some levels you can only size once in one direction then you can do it three times on other levels.
That mechanic of going inside or outside was interesting and added quite a bit of challenge which I liked. I feel like some times it was not very intuitive if I would get through the wall or will I just get pushed. But it was not frustrating so it didn't bother me.
Overall it was a great game, and I really liked it. I hope it might grow to a full game one day!