after you mastered a 360, you can start doing corky 3s by leaning in to the spin off the lip.
once you got that down, carve and pop the same corky 3. this is going to put you into the death spin, which is what you want. use your core strength to come out. let your feet go as high as you want, but to get flat you have to learn the perfect amount of carve pop and set. furthermore, pulling on my safety grab really helps control the trick and get flat as a pancake.