happened to me, almost word for word. new to competition, was told X start time, showed up early, etc..
after I left the site the day before the event, they changed the running order, nothing was posted anywhere... My division went from a mid afternoon event to first off the dock!
I had someone call me when I was preparing to leave for the site (1hr away) saying, "hey you're up next!". I was planning on being there for 4-5 hours before skiing, but I was now 2nd off the dock!
the difference between my situation and yours is I showed up, talked to the chief judge and he snuck me in to the rotation later in the day and I got a score for the books but I couldn't ski for medals as I was out of the division. no harm no foul. I ALWAYS make sure to be there at 8am or whenever the event starts now, otherwise I dont go.
I don't like that they didn't let you ski later in the day, no reason for that. We do this for fun, and there's a shortage of competitors, not an abundance. Hopefully all can learn from the situation and move on.