As others have said Garage Sail/Sale

, you need to bear away first.
I remember having trouble with these years ago, watching all the other local guys doing lay downs. One of the guys told me I was trying to lay down the sail too early. I think my reason for that had been to try and lay it down as soon as possible to allow for enough time to bring it back up again and master the gybe.
As soon as I started bearing off deep before laying the sail down I found it a lot easier. I find max speed, then bear off really deep, then lay down the sail by swinging the boom down like I'm going to chop my ankles off with the clew seems to work for me.
I reckon the sweet spot to lay down the sail is after you've bared away and the sail has depowered a fair bit but you still have plenty of board speed; that point where you're travelling on momentum rather than speed from the sail.
Crank it down hard, then rip it back up again and let go of your back arm as it's coming back up as you're now late into the gybe and want the sail to start rotating rather than you getting caught on the wrong side and slammed backwards into the water.