It sounds like it hit out of the blue. No wonder it was a shock, like being stripped naked in front of the church body.
It is another example of 'why' this subject needs to be discussed more. I am guessing that your pastor must be making a sincere attempt to extend a resource to the community by inviting this group to address the subject to his congregation. Since it is still your own private matter, it probably did not occur to the church leadership to give you a 'heads up' about the topic. It surely never crossed their mind that a survivor was in such close proximity to them.
If your pastor is trustworthy, this may be a perfect opportunity to talk with him in private and request a 'heads up' when a triggering subject will need your assistance in signing in the future.
Sounds like you handled the awkward and startling moment with wisdom and class. There is never any shame in taking the high road. Pat yourself on the back for making a good, sound call on the fly.
This is not a moment for beating yourself up and shaming yourself, this is a time to be proud for behaving professionally when you had the wind knocked out of you while standing in front of an audience. It takes a STRONG survivor to pull that off!