Many here have had that problem. It's the springs that pop the hatch when you release the latch with the button, they're too short.
Here's a thread:
!!For 370Z Owners with the Stuck Hatch Release Issue!!
Two fix options. Get the dealer to put in longer springs or invest $.04 for a quicker fix. I went with the $0.04 fix, works great
See the thread in the link for more info on both options.