Do you have a reloading manual? It would smooth this whole operation out because it would explain what the steps are in reloading a case and what each die does. Does the manual of the 550 contain any information about how to configure the press with dies?
The way I think you should set up your press:
Station 1, Sizing die, just screw it in according to the instructions
Station 2, Dillon powder through expander and powder drop, this should have come with the caliber conversion kit for your press. Adjust the expander so it bells the case mouth the minimum amount necessary to seat a bullet. That is, belled enough that you can set the bullet in the mouth of the case a tiny bit.
Station 3, Seat and crimp, the current die you have for station three seats the bullet and then crimps (eliminated the bell you just made in the case mouth to seat the bullet). Ideally you would not use a single die to do this, but the one you bought does. The seat and crimp die needs careful adjustment to work correctly. First thing to do is read the instructions that came with the die to find out how to adjust it. Second, configure the die so it does not crimp at all. Set the seating depth you want. Then after you have set the seating depth you can adjust the die for the necessary amount of crimp. Caveat, I have never had a die that seats and crimps in the same step so the procedure might vary a little.
Station 4, Here you should put the die that does the crimping, crimping in a separate step makes die adjustments easier because the two operations (crimping and seating) are no longer linked. Buy a Lee Factory crimp die to put in this station.
Take the expander die you got with the 3 die set and put it away. You will not be needing it for now.