Hello Aspirant

You should inform the University's authorities and the admission office about this mistake. This will create a problem for you in the future. Because this is a reserved seat for a single girl child and you took that seat, it will be considered fraudulent and the university may even ban you from their college and intimate this to the authorities that would not let you take admission in any college.

Above all this, it should be your duty to inform this because you took the seat of another potential girl who actually needs this. It is a subject of morality as well. Please inform the university about this. I'm sure that when you tell them about your honest mistake, they will understand you.