Answer:
Dear Zina,
Hope you are doing well. Felt really happy on hearing that you finally got admission into my formal school. It was big moment in your life and for that I wanted to congratulate you and guide on some points as well.
That school holds a great place in Society so its your duty to behave accordingly. Although the admission criteria is pretty strong you still need to be aware of bad influence. Enjoy your time there and make ure to participate in sports and drama etc.
Your kindly
Mark