Mashallah it is very good that you started HALAQAH at the masjid. Its also wonderful that you also started wonderful activities in the halaqah....The next step would be to call the sisters from your school to join the halaqah. This might be difficult. Try to incite them materialistically. Try to organize any event that interests the sisters. Ask the sisters in your school to come play with you...etc.....so invite them materialistically and after them give your message..