Great game ! I love the concept !
The "next level" button takes me back to the menu. I'm not sure if that's intentional, but it's not a big deal. As you add more lines, it can get quite challenging, but since you can't lose, it might be a good idea to add lives or a timer to increase the stakes.
PS : I noticed that you commented on my game "Switch", but I couldn't access your comment because I was resolving an issue with the organizers ( I had submitted my development build, and the game started with the final levels ). Now that it's sorted, you should be able to play from the tutorial, and please feel free to leave another comment...