The tense is fine, but in other than very casual situations you should use wasn't going to...
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Knightofsportswasn't gonnaIt's true that you can say it like that, but you always write it "wasn't going to". So you look at the words "wasn't going to", and you can say "wasn't gonna" (usually in casual situations). It's something like looking at "laughed" and saying "laft". You don't write it as "laft", but you say it that way.
Knightofs