Get in the pool!
I did my first triathlon about five years ago; a sprint distance and thought the same thing about the swim. It was horrible, being in the water with 400 other people and having not trained appropriately the swim ruined my entire race!
After that I joined a masters swim program and the difference was night and day.
Don't get me wrong, I am a slow ass Clydesdale just doing it for fun but the swim can make or break your entire race experience!
I was doing olympic distance the last few years until blowing my knee out playing basketball and gaining 50 pounds, but I'm back on track, got my knee reconstructed and got back in the pool. I should be running by the end of the summer!
Good luck with your first event!
Rangers Lead the Way, Hooah!