I entered neptune and locked the ignition timing at 16.5.

Afterwards, with the ignition timing gun, the mechanic adjusted the distributor until he finds the 16.5 with the gun.
And then I released the lock.

is it all correct what I did ?

 

As long as he actually set the distributor timing to 16.5 which is the value which you locked the ignition to, the timing is now synced.