Hi there,
Ignorance is not a sin, but there is such a thing as culpable ignorance. Once you attain age of reason you have the obligation to seek the truth and know the faith. If you are ignorant of things about the faith, which ordinarily if you wanted to, you could have known, then you are guilty of culpable ignorance. Just like if you are a student and you dont study then most likely you’ll fail if you sit for the exams and your punishment is that you redo the exam and dont move forward until it can be ascertained that you have acquired the required knowledge of course it’s not a perfect analogy