Another "must learn" is how to open the car when the battery is dead. Especially the boot, wherein lurks the battery. Tucked under the swab of the rear left seat is a pull-cord. That's your emergency boot release.
Try some silicone lub on the latch. Mine refused to open several times when I first bought the car - which gave me a right heart attack - I assumed it must be dodgy Italian wiring, but a little squirt of silicone seems to have cured it for the last few years.
The mechanism itself was sticking and just as dickygrace suggested above the second bout of pushing teh flap in seemed to release it. The mechanism looks a little grubby so some WD40 has been applied and it now works every time.