oh that's so weird, it seems the CGs show up in a different order for different people? I thought they'd be in the same order as in my gallery! That makes it really hard to figure out which ones you might be missing, but what I can think of if you romanced everyone and went through both Sun/Star is you could be missing:
(SPOILERS)
Thisbe's Leader check CG (unlocked by passing her leader check in Chapter 2's camp scene, some additional lines and the CG appear in Chapter 3)
Beca's Leader check CG (same as Thisbe but by passing her Leader check in Chapter 2)
Ikemma and Rhain's ending (unlocked by romancing Rhain, having Ikemma as your lover and choosing to leave the island)
The no romance ending (unlocked by not romancing anyone)
(SPOILERS END)
Let me know if that helps! I'll include a full list of all CGs and their unlock conditions in the DLC booklet I'm working on but it's a shame our galleries are in a different order, makes it a lot less straight-forward.