Can I just say, Woohoo for getting paid mat leave as a casual! That's great of your employer to offer that. As others have said, if it were me I'd be talking to the boss as my understanding of it was that except in special circumstances, employers aren't legally obligated to offer casual employees any mat leave at all - paid or unpaid.
This is just tops of your boss... I was fulltime for two years at my job and all I got was the leave, no pay