Most of the time I would say that your time to come out is up to you, but this is different. Even though you may feel that you are being untrue to yourself, if you show up in a gender that no one else knows about, all the attention is on you. Brides in particular have that one day to be the center of everyone's attention, and worry about things going well on the day. This is her day, one she will remember forever and hopefully cherish.
If you try to come out at her wedding, at best most of the attention will be taken away from her. At worst, it could cause an ugly scene. I understand why you want to come out when everyone is together and get it over with, but in this case, let the bride have her day and memories that she can look back on fondly.
sam1234