Green’s Dictionary of Slang

(Aus.) to make a mess of, to blunder.

1986		R.G. Barrett Godson 17: [T]he Vietcong had certainly stuffed up what should have been a good night’s tooling for Eddie.
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 245: ‘When you stuff up next time — and you will — that’s when I’ll be asking’.
1999		Sydney Morn. Herald 26 July 26/2: Their chief executive [...] stuffed up [...] But the Magpies stuffed up a second time.
2018		G. Gilmore Class Act [ebook] ‘The office keep stuffing up’.
2021		C. Hammer Opal Country 322: ‘He was strict as all fuck. Like he realised how much he’d stuffed up’.