You are free to continue with either name. They are both good names and parents are free to change their child’s name, or go back to using a previous name.
Ainul means “eye of” and Marzia means “someone that others are pleased with”, “someone that God is pleased with”. Ainul Marzia means “eye of the girl/woman that God is pleased with”.
There is no mention of the names of houris in the Quran or the authentic ahadith, therefore we have no way of knowing if whether Ainul Marzia is the name of a houri or not.