Friendly Plastic

I am waiting for the Gesso to dry on an altered book, I am doing with a friend, so on here trying to catch up with my craft journey.
I have been having a play with my friendly plastic, as I needed a break from buttons, Zettis, doodles, and jigsaw pieces. So, before I do my final pieces for my own jigsaw, I had a play.
The only trouble with gluing a lot of friendly plastic onto a card is it makes the card go banana shaped, even heavy weights won't get the bend out of it. I must have another go, and try something else