I LOST MY PX4 LOCKING BLOCK/NOT SURE WHERE IT WENT DURING REASSEMBLY?

More likely than not, your locking block is not lost:
It is fairly common for owners of the PX4 (full-size & compact) to accidentally re-install the locking block into the frame without the barrel and slide. If you think you have lost your locking block, look in the frame first. See the two pictures below, if you cannot look down into the frame between the front slide rails, it is because your locking block is in there. Pull down on the disassembly tabs on either side of the frame and push forward on just the locking block to slide it out of the frame.