All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If your father had gifted you without gifting his other children then he was wrong as he is religiously required to be just when gifting his children, males and females alike, as Allaah Says (what means): {Indeed, Allaah orders justice.}[Quran 16:90] The Prophet also said: "Fear Allaah and be just between your children (when gifting them)…" If the father died before being just in gifting his children, then the scholars differed in opinion whether the favored child is obliged to give back that gift for inheritance or does it become his property and it is not included in the inheritance? The details of this are mentioned in Fatwa 100312.
According to our view here in Islamweb, that gift is not valid and it is part of the inheritance.
Therefore, we advise you, dear brother, to correct the mistake of your father by giving back what he had gifted you to the inheritance, and this is better for you.
Allaah Knows best.