I'm here Brina whenever you need me!
I think you have a big leg up being a strong swimmer! That is most triathletes weaker leg, or the one that freaks them out the most. As I like to say "if you get tired biking you stop and coast, if you get tired running you walk, if you get tired swimming YOU DROWN!" YIKES ha ha ha
Remember the first one is all about going out and having fun! You only have a first one once you know, so enjoy it.
But yeah, Like Lise said- you have to train. I think too many people see others doing it and just "assume" they can too because they are skinnier than them or they hear things from charity groups that trump how anyone can do a tri/marathon/century etc.. So they just assume that it must be easier than it looks. Well, yeah- anyone can... With the PROPER TRAINING! Does that mean you have to go out and kill yourself everyday? Heck no. You just need to work up a nice base and you'll be fine. Every workout builds on another. The only real important thing about tri training is that you have to practice running off the bike. Even if it's a short bike and a short run, those first few moments matter. Your legs are like jello the first half mile or so, but w/ practice it gets better.
Ok, I'm rambling... Sorry... back to the couch for me!