The "pick list" is whoever your parents put when you enrolled in the school district and that remains constant throughout your time in district. They can also change it. Perhaps OP parents got the Aunt put down on the list? Or maybe OP added her as another person if the school allows that. Just depends on their policy.

Second, OP parents gave the Aunt guardianship, the parents did not give up their parental rights so by default, yes they are still on the list, and no, OP does not get a say in that because legally, his parents have a right to her still.. So if OP parents decided today to kick up a legal shitstorm, the Aunt would have to take it to court to hold on to OP.