Take heart, it's actually not as complex as it appears at first glance, and could definitely be harder. Usually, with language learning, you hit walls, and you struggle for a while, but then you have a breakthrough and it all makes sense.
Keep at it, and don't get discouraged. It will do wonders for your brain and for you as a person.
That is wrong.
1) Тетрадь is the singular form and it is a feminine noun, so it would require моя instead of мое.
2) This Russian sentence is in the plural. The nominative plural possessive pronoun Мои sounds different from the nominative singular possessive pronouns and the plural form тетради sounds different from the singular form тетрадь.