You should be able to cut back. I use my 28L bag for 2-3 night weekend trips, with my 20 degree quilt inside. Replacing items with UL gear will lighten your load and also create space. Obviously that's an expensive route, but maybe less than a new pack. Another tip is going through your pack and bringing only what you need for the trip. For me, I saved a good amount of space by only bringing a few first aid supplies instead of the full bulky kit. Same with water filtration. That said, it's tough for me to go more than a few days with 30L unless it's summertime.