I don't know what form it is that you filled out BUT when my husband and I first moved in together, my husband didn't think to inform Centrelink because the money he was getting was related to him being a student and basically he didn't think it had anything to do with me...
Before we went to apply for our spouse visa, I made him contact Centrelink and explain so that everything would be in order for our spouse visa and nothing would look dodgy. We'd probably been living together for less than a year when he changed it. I got my spouse visa no questions asked but we did have to pay Centrelink $200 a month for over a year, maybe close to two years, because my husband had been overpaid. My advice would be correct your mistake NOW.