Welcome Mark-
Don't get too down on yourself, every one of us has probably gotten clobbered at one time or another. Sometimes, you just get a bigger than expected crowd. Some things I always had my staff do are as follows. You don't want them to have to be stocking/etc, when they should be selling. So make sure your stand is stocked up completely before the people get there. This includes little things like napkins, straws, seed oil, every item you use. Make sure your ice bins are full. Open popcorn bags ahead, make kids trays ahead. Make sure the soda syrup bibs have been checked, anything that might go out during showtime, have a replacement box on the rack, open and ready so you just have to move the connector to the new box. Look at your menu board, is it easy for customers to read and understand? Are sizes/prices clearly visible? Nothing worse than customers slowing things down themselves, because they haven't figured out what they want. Do you offer combos? A large majority of customers will get used to ordering a COMBO, thus making the sale faster. Do you have your employees trained to work FAST, get the order, get it served and on to the next one...Also, when I ran a single screen second run theatre that was very busy, I sometimes would start the movie a few minutes late 5-10 at the most if their was still a large crowd in the lobby. Most people understood.
Just a few thoughts.
Jeff