One lady said that she thought I can't backtrack (ticket type LLONE4). I told her that i thought the advantage of the ticket was that you COULD backtrack within a continent.

Is this ok

(coming in from London)
Lon -> Chicago
Chicago -> Mexico City
Mexico City -> Cancun
Cancun -> Miami
Miami -> Mexico City
Mexico City -> Miami

(southwest - no oneworld flight to get to LA)
Los Angeles -> Sydney

Also - my ticket originated in Perth, is it fine to Terminate in Sydney?

Thanks!!