@Fernweh explain firmly to your breast surgeon that your mental health will be at a huge risk if you do not have both breasts removed whilst having the surgery this Thursday, if that is what you truly believe is the case. Don't back down, your mental health is very important, and they will be responsible if they don't listen to you, and you end up in the psych ward because you can't cope. They need to document your desire to have both breasts removed this Thursday. Be pushy if need be.
The doctors need to listen to your reasoning and you are the one that knows yourself better than them.. If you end up in the psych ward they will be responsible. Not saying you will, but they need to listen to you, don't let them try to placate you into believing they know better.
I remember saying when I was not sure if I needed one breast removed or both, I firmly said if one is to go , I want both to go, and he could see my determination, and said he would remove both if I wanted that. Long story, but this is about you and please stick to your guns, so to speak.