I would suggest trying to recreate the problem, using a key pair for testing only.
look at what you wrote down as the passphrase and think about how you could have erred.
... implicit errors in "writing it down."
Examples are.
"C" or "c"
"0" vs "O" vs "o"
"l" vs "1"
"7" vs "2" sometimes
presence or absence of a space between words
a missing character
transposed characters
Yesterday I wrote a note on paper. "Here is the summary."
Today I looked at that note and it said "Here is the summy."
Go figure....