You know that 不孝 means "disobedience to parents. So, if you add parents to it, it just means the same thing. Just a longer version of the word, basically. This means lack of filial piety or disobedience to parents.
The reading for 不孝 is the one you learned. Then, add 親's reading (vocab) to it.
It’s already too late, but I was a really disobedient son.