The accident Bu by Reported inconclusive due to no evidence
It sounds to me like they believe you probably are guilty of the accident but can't pin it on you for whatever reason.
They then intentionally over dispatched you to get your attention, but instead of calling for help since you were buried, you got sloppy and now see the result of trying to accomplish the nearly impossible. It's a rookie mistake.
At panel (discuss this with your BA extensively prior to that) you're best bet is to be very apologetic and explain your confusion due to the heavy day and your inexperience. JMHO. I can buy your story, if in fact the accident charge was bogus and you've been honest with them on it. If, on the other hand you're in the habit of making things up as you go, they'll eat you alive at panel. Count on mgmt to bring the accident and anything you may have left out here that is a negative in your personnel file to your hearing and using it to paint you as a bad guy.
I hope you are being up front here and will be there.
Good luck.