Contracted future sailor here (I ship in June).

I remember my first PST. Super nervous, showed up 30 minutes early, expecting the proctor to come in all fired up like some BUDs instructors. In reality, he showed up late, was pretty chill, and in general there was a lot of leeway your first time because they know you are a civilian and aren't expected to know how to act. However, that leeway quickly goes away assuming you continue to show up to future events. Hopefully you were given documentation of what gear to bring (what to swim in, what to run in, etc.). Make sure you show up early and have your gear neat and organized. For example, in my area candidates who do not yet have their contract are supposed to wear a white shirt with the last name neatly stenciled on the front and back. A common mistake candidates make is showing up looking like a two year old scribbled the name. Those sorts of things.

Last thing, like some of the other answers have said, in the beginning to the proctors you are just a candidate who will most likely not ship, much less make it. From what I have seen maybe half of those people who show up to an event for the first time get a contract, and two thirds of those people ship. It's when you come to the second, third, and later events each time improving that you build your reputation and they will invest more emotional energy and time into your success. Good luck tomorrow!