Pics https://ibb.co/album/sbjqwT (the weird triangle on the lower piece was fixed afterwards)

I’ve been messing around with a press mold so I can make hex tiles using paper mache, or something else that is easily and cheaply available.

The problem I’ve been having is with the sides, which rarely get properly pressed. What should I do to possibly fix this, regarding the model?

Right now, I’ve only experimented with minced paper and water, which led to satisfying results. What other things could I add or try for this kind of press? What could I apply on the mold to make the paper less likely to stick? Vaseline doesn’t make a difference.