I must be doing something wrong! I have been doing some trial packing for an event next weekend using the 100 litre Berghaus Vulcan. A bare minimum loadout completely fills it!
Not necessarily doing anything wrong. Much will do to what kit you own ~ a big, warm, sleeping bag can take up a lot of space as can a bed roll and a tent / shelter. If you're a big lad or lass then any spare clothing will take up more space than if you were a racing snake. The size of cook sets varies massively too ~ do you boil in the bag or cook?
If you're just taking what's required for the event then you're (probably) carrying the correct kit in (probably) the correct sized pack but, on the other hand, if you're concerned that you're taking too much and would like input from others, whack a thread up