I'm really scared about my braces... Please comment.?

Hello, first of all I am from the uk if that makes any difference. Ok so basically I have had my braces for a couple of days over a year. I am getting them off tomorrow and I am terrified that I will get marks where they were. I brush twice a day for 3 minutes as I was told unless there are exceptions e.g it was incredibly tired etc. Buuuttt I don't use mouthwash and I eat quite a lot of chocolate. Will I get marks and the reason I told you I was from the Uk was because I wondered if they whitened your teeth after if there are marks. This boy in my class had his taken off a couple of months ago and he goes to the same orthodontist as me and his teeth looked perfect and very white. Another thing is I chipped my tooth about seven years and something happen and the bottom of my tooth went yellow so now I have a yellow mark on it. Will this make everything look wierd? Thank you so much xxxx