Can't get back to shed

Hi there, I need to go back to the shed now but the game won't let me and says I have to find Jason first. Am I missing something? thanks!

I started over and was able to go back. The only things I did differently were that I didn't try to go back before I needed to, I didn't put the skulls on the floor and I didn't put the picture parts in since I only have 3 of the 4.