One thing that I learned and helped me was to only think about swimming from bouy to bouy. It helps break the swim up into "doable" legs. Also, if you start to panic just roll over on your back and float--look at the sky and that will help calm you down. I thought i was going to panic but I didn't. I found that most of my anxiety came prior to getting in the water and once i was in there and swimming it turned out to be rather easy. You will do great. Try to relax and have lots of fun.