I really enjoyed this puzzle game! The polish is really good for the time, even something as simple as restarting the level has a fancy animation and sound!
The puzzles are really hard, which is alright, but if you continue working on this game (which you really should!) you should add more easier levels in between so it doesn't get hard that fast. btw I obviously understand that 12 levels are impressive for 48 hours, especially because they are so well designed!
I also love being able to undo - it really helps! Also, I know many people have pointed this out already but the UI could do with a makeover if you do continue working on this game.