Talk it over with your parent. Make a plan for any and all possibilities if it makes you feel better. Knowing where you'll be when the transplant happens gives you some security. When grown-ups are frightened, they sometimes act angry. When teenagers are frightened, they also act angry.
Fear is scary.
Anger is relatively easy. Talk to your parents about what you're feeling. My mom was sick for a long time. My brother would storm out to be with his friends and I'd be left to fix meals, clean up and take care of my younger sister. All that with homework too.