I only realised two years later after singing the wrong line proudly and confidently for ages! No-one wanted to tell me I'd got it wrong because they thought it was funny.
I only found out when my mother corrected me after what must have been the millionth time I'd sang the wrong lyric. I was so embarrassed I haven't sang the song since!
Still, it's a good song. I think I'll be singing it again :P