Assuming, for argument sake that you are a national system employee (although if you're based in WA and are not employed by a company, you would be governed by state laws). In accordance with the NES less than 12 months continuous service has a minimum notice period of 1 week.
Your contractual notice however is 12 weeks which suggests that if you do not provide the required notice and terminate the agreement, you would technically be in breach of the contract and the employer could seek damages.
Can you give a little more info regarding the situation, is the 12 weeks respective and mutual or just applicable to you ?