To cancel an order, you will need to go to Portfolio> orders > status and click cancel.
If you have submitted your order as a market order, the order may be filled quickly so be mindful that your may still be processed even if you wish to cancel. If you submit a limit order, you will likely have more time to cancel depending on market movements and the price you wish your order to be filled at. If your order is submitted out of market hours (10am-4pm AEDT) then it won't be filled until the market opens.
If your order does fill, you will still have the option of buying or selling your shares, keeping in mind brokerage costs will apply to any buy or sell transactions.
How long does it take to cancel an order?
Cancelling an order should only take a few minutes from when you cancel to when the funds return to your wallet. If you can't see the money returned, you may need to refresh the app page.