The Rosso twins are
Join Date: Oct 2011
Location: United Kingdom
County: Tyne and Wear
There will be a micro switch inside the latch mechanism that will detect when the boot is closed, guessing thats got damaged when you tried to close the boot.
Sounds like your alarm is warning that a lock isn't closed, hence the extra beep, there is also a warning on the dash light for the alarm, it flashes to tell you the fault.
Could try and take it apart and see if it can be fixed (never tried to do it so no idea if its possible although I am sure someone will have had a go), or get a new latch.