Is there an expiation for my sin of fornication and disobeying my parents other than seeking forgiveness and showing remorse, and how can I be sure that Allah Almighty has accepted my repentance?

The expiation for fornication and disobedience to parents lies in remorse, a firm resolve not to repeat the sin, frequent seeking of forgiveness, performing good deeds, and adhering to the piety and obedience of Allah. In addition to this, the disobedient child should seek forgiveness from their parents and strive to please them.

Allah has promised forgiveness to those who repent and mend their ways. Allah Almighty says: "Your Lord has decreed upon Himself mercy: that any of you who does wrong ignorantly, and then repents after that and corrects himself - then indeed, He is Forgiving and Merciful." (Al-An'am: 54) And Allah Almighty says: "And whoever does a wrong or wrongs himself then seeks forgiveness of Allah will find Allah Forgiving and Merciful." (An-Nisa: 110) Moreover, piety and good deeds expiate evil deeds, as Allah Almighty says: "Indeed, good deeds do away with evil deeds. That is a reminder for those who remember." (Hud: 114)