I really like the direction of this game, but it's just a bit janky/confusing at times. I'll try to give as much insight as I can to help you make it better because I think it definitely has potential!
First off, thank you for adding a description with instructions. I think it's really important to let people know how to play your game especially if it has unusual controls. Though, I suggest adding some more information on the popit menu.
About the popit menu, it has a nice opening animation and looks fairly simple, but I feel you should be able to choose where the new block will appear. And sometimes choosing clear square deletes all squares on the level.
Another thing is, the space to build the level is a bit too small. It would be cool to have a scrollable camera, and/or an option to decide how big the world should be.
A few minor suggestions is allowing the player to choose what kind of square/object to place, adding premade enemies/obstacles, etc.
tl;dr this game has a lot of potential, but I suggest making more fixes before you upload a new version to make it enjoyable!