I make mistakes — I’ll be the second to admit it.

Jean Kerr (1922-2003) American author and playwright [b. Bridget Jean Collins]

Essay (1958-07), “Hand Me My Dark Glasses,” McCall’s Magazine
    (Source)

Collected in her The Snake Has All the Lines (1960) as "I Was a Sand Crab."

The original in McCall's has what I suspect is an incorrect "correction" from an editor, reading "I'll be the first to admit it," which is not particularly funny. The "second" text appears in the book.