Nerves are a very normal part of this surgery. It's no fun, but is another thing to deal with when getting ready for surgery. I was nervous right up to the moment I was put under in the OR. Keeping busy until the day of surgery helped; if I had any down time I'd think about the surgery, which would just make me even more nervous, so I kept as busy as possible.
The good news is, this time will pass, you'll soon be on the other side and on your way to taking your life back from a painful knee(s).
Which knee are you having done?