Hang in there. When I got close to "the day" I seemed to all of a sudden feel very calm. I realized that all of the decisions had been made and there wasn't anything else I could do to affect things. I just accepted the fact that I would "sign myself over" to my medical care team, and then the next time I would awaken I would be "on the other side of the mountain." Once I realized that I could no longer affect the outcome, I just got on with it.
Think of it this way -- if you didn't really need this surgery, you wouldn't be at this spot in the journey. You need it, and life will almost certainly be better after than it has been of late. I wasn't sure about this last part, as I had been quite active right up until the week before - including jogging daily, etc. Fast forward 3 1/2 years, past some crummy speed bumps in early recovery, and now life is truly better than it was in the year or two before surgery. No, I don't run any more, but that is no fault of my heart. (My knees won't take it any more.) I am still in the gym 5 days a week, and can do more of almost everything now than I could before.
You've done all the worrying you need to do. Just go with it now and come on out the other end and tell us about it. We will be here for you.