Green’s Dictionary of Slang

an excl. used on dropping something, tripping over, bumping into someone or something, making a mistake, being surprised etc.

1934		(con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 209: Ooph, that’s a hot one. [Ibid.] 397: ‘Ooph!’ Studs exclaimed, seeing Dapper Dan O’Doul in a football outfit.
1949		Wodehouse Mating Season 147: Backing away with a startled ‘Oops!’.
1959		Dandy 26 Dec. n.p.: Oops! Gosh! I’ve upset another Santa!
1968		Dandy 30 Nov. n.p.: Oops! Here comes the guide.
1977		E. Bunker Animal Factory 41: ‘Thought there weren’t gonna be any questions, boss.’ ‘Oops, that’s right. My apologies.’.
1977		S. Kernochan Dry Hustle 29: Oopadoop, I gotta scram now.
1987		Beano Comic Library No. 124 54: Oops! I think I blew it!
1999		Indep. on Sun. Real Life 6 June 3: If you drop in words like humongotarian, oops, I mean humanitarian.
2000		Indep. Rev. 20 Jan. 7: Oops, sorry I spoke.