You can if you like, but since it's only taking 3 days to process most applications, it's probably not worth the extra $300 for priority.
Since you have already applied and paid and did your biometrics, it's best just to let the application stand and run its course. Hopefully it will be approved and you get your passport back within a week of sending in your supporting documents. It's possible that your case attracts extra processing time and you won't get your passport back in time, in which case you have to withdraw your application in order to get your passport back and lose all your fees. They do warn applicants not to book a non-cancellable travel before getting your visa, and this is the risk you have taken, but I hope it doesn't come to that.