Flick harder but don't over think it, when I tre I focus on the motion as a whole meaning the entire trick at once, what seems to be your issue is just stay centre over the board and timing, just commit you got it👍🏽

It could be helpful to try jumping a little bit in front of you for the first times, focus a lot on the scoop, flick is not really essential in 3flips, it just helps :)