I'd have thought it would be a quiz night i.e. tables of 4 or perhaps 6 to make teams. If you are alone, the organisers should find you a place to sit to make up a team. It shouldn't be anything too formal, perhaps with fun prizes if anything at all. Take some money in case there's a charge for each round of questions. Was there any mention of refreshments? At our parish, we bring our own, but if they are sold at your parish, definitely take money to buy something, even if you are not hungry, so that you don't feel awkward while everyone else is eating.
If it's well-organised, it should be a really nice way to meet people as a singleton. If no-one thinks to steer you to a table to make up a team, would you feel able to just say to someone that you haven't a team to join?
A tip, though - don't arrive late. If anything, be early and offer to help with putting tables out.