Hi Pat, my surgeon told me if all else was ok, they would do a mini surgery on me, however, when I woke up, it was the full "zipper". I too was very stressed out because either way, it is a major event! I had my aortic valve replaced but chose a tissue valve. If you are stressing too much about it, ask the surgeon or his staff to get a prescription to relieve the stress. I'm sure they would happily do it and it would probably make the days leading up to it easier. I will do that if I ever have to do it again.
As far as my scar goes, it is barely visible so I am ok with the way it turned out. My rationale was if the chest is opened completely, it allows the doctors the most access.
Either way, have faith the doctors have done it many times and for them, it has become almost routine! Best of luck! My surgery was Aug, 9, 2012 and it seems like a long time ago now!
Mike