Being nervous before any surgery is very normal. I don't think you can change the nerves, but you can keep yourself as busy as you're able getting ready for it. I used my pre-op time to make a lot of meals for after surgery, I made sure my house was ready for me post-op and made sure I had all my recovery aids ready to go. The busier you can keep yourself, the quicker the time will pass.
As for post-op pain, make sure to have a thorough conversation with your surgeon about your concerns for pain control. Ask him what he will be prescribing, for how long and make sure he answers your questions to your satisfaction. Some of us have pain for a longer time than others; we never know how much pain we'll have and for how long. I know after my TKR I had a lot of pain for a long time, but after my revision I had very little pain after about 2 weeks, which is very unusual. It was actually a miracle for me due to my particular circumstance, and one for which I was very grateful. But people have varying degrees of pain, and for varying amounts of time; in my experience most people have pain that lasts longer than two weeks.
Make sure to have a good icing method, whichever one you choose, as ice and elevation really do help alleviate pain. It was my only source of pain control after the aforementioned two weeks; even though I had very little pain, I did have times when it would spike (usually after activity) and the ice machine/elevation combo really helped deal with that.