The way undo works changed since last time but I'm glad you can still activate it using a not-so-secret secret because sometimes I press a button twice on accident and really need it then.
I tried not to abuse it but it probably helped me. New high score: 1720. Definitely got exhausting at the end, really got drawn out... but hey, it's a high score :D
Also, this game was totally impossible at first when I didn't read controls/rules.