Double check that something is not covering the bar that latch grabs onto - check that the lower trunk trim hasn't shifted and covered that bar.
Check the latch itself, make sure that it didn't accidentally latch itself (should see an open "V"). If it is latched, or it is hard to tell - can always put in your key into the trunk and unlock it again. That will ensure the latch is not engaged.
Try closing your trunk and see it latches now. If it doesn't - possible that there is something physically causing the latching to fail - could be a bolt has shifted, moved the alighment of the lock so it cannot grab the lower bar. Possible the trunk latch is damaged or the remote cable is snagged - have to pull that cover plate off to view the locking mechanism. Don't have to be a lock expert to visually see something is messed up (ie, something that is broken, cable dangling, etc.)