I assume your car has the original vacuum central locking and it works? if so...

The lock has 3 positions ..

Key upright...boot remains locked irrespective of central locking

Key horizontal...(left 90degress) boot is locked/unlocked with central locking

Turn another 45degress counterclockwise (from horizontal) and press in will unlock boot if central-locking is 'locked'

Looks like you may have messed up the activating plunger when you re assembled it, on my car this plunger/washer thing was a loose fit.. try parking it so that the one side is higher than the right.. turn the key all the way to the left and try pressing the button, after that try with the other side raised instead. The more severe the angle the better. theres a slim chance the activating plunger might move just enough to get things working.. thumping the boot during the whole process should help.

Last resort... you have to sacrifice you right rear light... not too expensive and a better option (to me) than cutting a hole behind the number plate .

Best of luck

Anil