I was going to also say that the tampon would not likely be OK, since it would alter the normal functional view.
I have not had this particular procedure, but have had numerous embarassing things done to me (as I am sure all of us have). Being a nurse, I've been on both ends of it. Believe it or not, the staff get embarassed too, and they cover it by being very professional and matter-of-fact. These things are awkward for everyone.
It is OK to tell the staff that you feel nervous, self-conscious, or whatever. They will do their best to make you relax. I suppose the one saving grace is that you are in a darkened room.
Hope you get some answers at the end of the day to make it worth your trouble.
Jan