Things could go badly or well no matter which choice you make.
A. If you email your parents to explain you're trans and how you have felt all your life, etc., they could:
1. condemn, attack you, reject you, or even evict you.
2. accept you, get used to the idea, then agree to allow you transition this year.
B.Keep quiet and live as your birth gender. This could cause depression, anxiety, and gives unwanted hormones a chance to change the body.
C. Go to the GP in secret. Your parents could:
1. never notice, never ask questions
2. find out and attack/reject/condemn you
3. find out, but accept and forgive you.