Shoot me now

I've gone and signed up for a triathlon next month. It's not Ironman by any stretch of the imagination, just a sprint length event (a half-kilometer swim, 20K bike and 5K run). I do all three disciplines, but not typically all at once, nor have I ever done a competitive open water swim, but I wanted a challenge before my birthday at the end of July, and this one takes place in my home town, so I'm familiar with the route, but still... I've never done a real triathlon before (just an indoor one in the spring) and I have no idea what I'm getting myself into.

My only goals? First, to finish, and second, to not finish last. I figure that's about all I can handle at this point.

Anyone out there with advice? Psychiatric guidance?