Past kufr due to ignorance

Assalamu alaikum shaikh. I have a question. Many years ago I thought that I would commit kufr. I was influenced by a story and imagined myself as Allah, but I did not know that this was kufr and shirk. I believed that in the future I would really become Allah. If I had understood that this was shirk and kufr, I would never have made this mistake. I thought it was a major sin. I was completely ignorant of what shirk and kufr were. Later, after some time, I realized my mistake, but I did not repent and did not make that mistake again. Do I have to answer for it and were my prayers and supplications at that time valid and accepted? I have heard that if someone commits any shirk or kufr but he does not know that it is shirk or kufr. He knows that it is a major sin. Then he does not have to answer for it and his prayers and supplications at that time are valid and accepted.