Go back in time

I don't really know what event I would want and go back in time and change because I have a really good life. But I think that I would have to go back and tell my mom that she was having my sister so she would not take her diabetic medicine. You see my mom didn't find out that she was having my sister until she was six months pregnant and my mom was taking medicine that affected my sister's heart. When my sister was six months old she had to have open heart surgery. If my mom new that she was pregnant my sister wouldn't have to have heart problem.