Cousin marriage is not banned.
Sa-Gotra cousin marriage is banned.
Your father's sister's daughter, or your mother's brother's daughter - belong to different gotra (that of their father's), so marriage between these type of first cousins is allowed.
But your father's brothers' daughter is same gotra as you, so she is like a sister, so that marriage is ...
Customs will keep on changing with times.
Marriages between cousins may not be prevalent in present times in Northern parts of India. However, it is an accepted form in Southern parts of India.
Even in Northern parts of India marriages between cousins was order of the day in ancient times.
In Mahabharata there was a mention of Kunti, sister of Vasudeva ...