Searching for sibling born in 1975

[FONT="Comic Sans MS"][/FONT] I am searching for my younger sibling born in or near Charleston, South Carolina in (I believe) September 1975. My mother said she went through a Catholic organization who found adoptive parents. After the birth, the hospital staff told her she had given birth to a boy, but several weeks later she received a card congratulating her on the birth of her "baby girl"! So, I am unsure if I am looking for a brother or sister at this point.