Hi CaramelPuff! Thank you for your comment and I'm so sorry it took so long to reply!
I'm so glad to hear you've enjoyed the game!
As far as the last three CGs...
Without giving it away completely, remember that there are extra options in Adam's route, and one of them will give you the chance to get a second, different happy ending with him. Two of the CGs are unlocked this way ^^
The third....is my bad >.< it's literally just the 'locked' standard jpg that I left in there after testing to make sure it worked, because I am absent minded!! I'm so sorry for that, haha!
Best of luck obtaining the other two that you need :)