G'day,
You have almost certainly been ticketed; this normally happens for red e-deals within a few minutes of completing the on-line booking process and if not, within the next hour or so.
Note that any change you do: 1) Will incur an A$38.50 change fee, and 2) Can only be used towards a fare of equal or higher value.
I'm not sure why it's not showing up with a cancel button. You should
be able to. You may need to call Qantas. Tell them the on-line option is not working and ask them to waive the A$5.50 'phone service fee.
Other than that, do you see a 'Cancel Flights' button? If so, you can use this to cancel the flight and record a credit against you Frequent Flyer number/booking reference.
This can then be used as a credit (less any fees) for another domestic flight.