You're not alone, it's the first really difficult level in the game, despite using only the basic mechanics (which is why it's relatively early in the game). Anyway, the intended solution puzzle is here (spoiler): https://imgur.com/a/FiXOIMC (it's probably the only solution, if I don't count swapping the colors or putting something in the 2 empty squares).
I did consider making it easier, but I want the game to have a couple of really difficult puzzles, which is why I made this level optional instead.