I wasn't holding down the down arrow, I was holding up right and jump at the same time.
Also it wasn't a bug that made me stop at day 11, had to go to work and it was getting real hard(but not bad, just difficult)
Viewing post in Grandma's Garden jam comments
I think I figured it out. You were pressing dash a few frames before pressing up, and although there is a frame window of 10 frames (people said it was too hard) it didn't reset the dash timer, so you got less height. And because the dash is only ~20 frames, and itch makes the game run on a lower framerate, it becomes an issue. Fixed it, thank you for letting me know! Also, if you wanna give it a crack a again there is a bit of dialouge at the end :)