Had a strange trade executed today during the close. I won't mention the stock but here is the scenario with very similar numbers
Stock XYZ opens at 5.50 and I place a sell limit order of 2000 @ 5.55 (not to expire today). I see the market depth increased to ~7000 @ 5.55 after my order.
Stock fluctuates between 5.30 - 5.50 all day up until 4pm but closes 5.55 right after the auction. Later, checked my account and found out I was only partially filled? That's fine but the strange bit was that the volume during the close was 90000?!?
Why was I only partially filled?!? Correct me if I'm wrong but I thought it was first in dressed best OR maybe I've completely misunderstood this game and whoever has the largest pending trade (price * shares) in the queue gets first dibs?