Seems obvious now, but I had the same issue first time I
took mine off.
The sides of the panel (where the two small screws near the
vent are) the panel is designed to bend outward like a spring
into the quarter panels. You need to press lightly on the vents
and squeeze the panel out from under the quarters. Think of
it like a medicine bottle cap. Then there are three bolts behind
the plate. Then you need to go inside the trunk, pull the carpet
and remove the hatch lock. Once you remove the lock cylinder
the panel should pop out. It may be tight and put up a fight,
just be sure you don't scratch the hell out of the top of the
bumper cover. Good luck!