The answer depends on whether you are transferring from within Sydney, or from outside.
If you are transferring from another course at Usyd, all you need to worry about it doing really well at that course, as they will pick either your ATAR or your uni marks as a basis for transferring. Really well unfortunately means upper distinctions and high disctions, basically 80+ normally.
If you are transferring from another uni into Usyd, it will be more difficult because it is 50% ATAR, and 50% uni marks. You will be less competitive here, because your ATAR is lower than most people hoping to transfer and therefore uncompetitive.
Of course, doing the JD (postgrad) is always an option, and you'll definitely get a credit average with an ATAR like yours.