Was my action of fleeing the mixed-gender school and going to the mosque wrong, and how can I convince my parents of the prohibition of mixing in the absence of an alternative, and is it permissible for me to emigrate to Islamic countries without their knowledge?

It is impermissible to study in co-educational schools and universities due to the ensuing corruptions and prohibitions, especially in Western countries. If a permissible alternative exists, then co-educational study is not allowed, and obedience to parents in this matter is not obligatory, because "there is no obedience to a creature in disobedience to the Creator." If no alternative is available and the parents insist, then it is advised to be patient and strive to avoid places of mixing and to seek righteous companionship. As for emigration from the lands of disbelief, it becomes obligatory if a Muslim is unable to openly practice their religion and establish its rituals.