Signed up for a class online several days prior to...

Signed up for a class online several days prior to the class. I arrived on time, and was TURNED AWAY because they were at capacity. I am sorry, but I signed up ahead of time and if you have a room capacity then you need to turn away last-minute walk-ins!! This is terrible management and I had been looking forward to this class all day and now my evening is spoiled. I would like someone from management to address this really ridiculous issue. Thanks.