When I was a young swimmer I used to get super nervous about my swim meets for days to the point that I often arrived to the race with a cold. I did not know why but I of course now figured out that so much stress was actually compromising my immune system. Even as a beginner triathlete I still had quite the nerves prior to the race. It took a long time to learn how to cope but in most of my recent races, including Kona, I was very calm and my nerves barely played into the equation. Now I have two kids who are starting to compete in high level kids athletics and travel out of state for competitions. They get nervous and my job as a dad is to help them deal with the situation. Let me pass on to you some ideas that you may be able to implement should you need some help in dealing with pre-race stress.
Do not create additional stress. Get your equipment ready with plenty of time; arrive on time so you do not have to be frantic about missing a meeting or not having your bike ready. Much of this kind of stress can be minimized by simply planning well and taking care of all items well in advance. It would be a good idea to have a list that you can check off.
Visualize the race and your performance. Think about all the things that you need to do and have done in practice. Where are you going to line up in the swim? How many turns on the swim? Where is your bike located in transition? Where are the hills? Think about your strategy for all of this and have a positive outlook as to how you will deal if all goes perfect.
Be open and welcome challenges. Although we can visualize a perfect race we also need to be open and expect that it will not be easy. Almost every race brings a situation that is unexpected. You may not have a solution but with a clear head you can often figure it out and have a successful race. This happens to everyone including the professional athletes that win. You may not have a perfect race but you can race it perfectly.
Do not base success on a finish line time. Triathletes are very proud of their times including myself. However, time is only relevant on the specific race day and on the specific race conditions. One of my best swims in an Iron distance race is one of my slowest when looking at the clock. Be flexible and if you use time as a goal have an A goal but also a B and C goal that you can live with. Do not chastise yourself knowing that conditions can very well be the reason you are not meeting your A goals. Better yet, reserve judgment of your time and performance until the race is over. At that time you can look at all the information and determine how well you actually did.
Carry on with daily activities. Do not make all activities prior to the race be all about the event. Register and visit the expo but do not hang there all day listening to what everyone did or did not do. This has nothing to do with your race and more than likely will just put doubt into what you did. Get away a little bit and try to carry on as usual. Spend time with loved ones, more than likely they supported you along the way.
Finally remember that there is nothing you can do about everyone else's performance. More than likely they are going through the same thing you are going through. If everyone else is fit and are going to beat you then more power to them. Just concentrate on what you can do. Do not beat yourself up before you start. You did all you could do and the past is the past. You have a race to do. Take care of it and once you are done realize that everyone that loved you and liked you before still will. Those that did not love you will not change their mind because of your performance. Enjoy your race.