Failing at flush setting

I’ve been trying to set a 3mm CZ with very little success. I have set 2 as seen in the picture above, but ended up shattering them and they move around.

This is what I’ve been using (in this order): -1mm drill bit -1.5mm drill bit -2.5mm ball burr -3mm ball burr -3mm setting burr

I’m not sure if the seat is too deep for the stone or if I’m burnishing incorrectly but would appreciate tips.