Of course, it's not your fault, because it's impossible for anyone to spell accurate Cantonese pronunciation in Mandarin or Mandarin Pinyin, and it has nothing to do with Cantonese.
Because most Cantonese pronunciations have no homophones in Putonghua, even Putonghua Pinyin is invalid for most Cantonese pronunciations. Many Cantonese pronunciations can't even be found in Mandarin, so you can't spell the correct Cantonese pronunciations in Mandarin or Mandarin Pinyin.
If you must have that kind of unreliable homophonic lyrics, do it yourself. After listening to a sentence, use the word or pinyin that you think is closest to it. Just like your example, you can't do it, and no one else can. No one can pronounce it correctly anyway. There is no essential difference between you and others.
The most practical and simple way to learn to sing Cantonese songs is to sing along with him. Just listen and practice more. There is nothing you can't learn.