I'm a hardcore introvert who rarely gets lonely, but it does happen occasionally.

Similar to your school function, I find it helpful to have one regular, structured event in my life that forces socialization.

For me that's a tabletop gaming group - we meet once a week to play. The structure and shared goal is helpful, because it takes the pressure off of pure socialization. If I'm feeling social I can crack jokes & banter during the game, but if not I can just focus on playing.

Also, a weekly cadence means that missing one session doesn't make me feel super lonely, because I know another is coming soon. Your function sounds tougher since its only once a year - you might be better off finding a similar activity that happens more regularly.