Do I bear a sin, and what should I do about the days I missed in Ramadan due to menstruation in my youth out of ignorance? And do I have to make them up before the next Ramadan, even though I don't remember their number?

If a girl menstruates at nine years of age or older, she is considered an adult and is bound by Islamic rulings, such as prayer and fasting. Therefore, she must make up for any missed fasts of Ramadan (definition). If she does not remember the number of days, she must strive and investigate, and fast what she believes will absolve her responsibility with certainty. She is not obligated to pay expiation for the delay if she was ignorant of the prohibition of delaying. However, after knowing the obligation of making up the fasts, it is not permissible to delay except with an excuse; otherwise, expiation becomes obligatory, which is feeding one poor person for each day.