I think you could piece the pieces of insulation board and hang them gently with Command Strips until you can finish it the way you want it. I agree with the others, I have 2- 4ftX8ft sheets on my wall and it often is not big enough. Think I'll start doing smaller projects

Have you looked at "Heavy duty design wall" By snowbird posted on 5/16/2016? She uses the whole wall because she starts at the top of the wall, and doesn't use styro boards, Worth a look.

A thing I would hate to do - but my DH might cooperate if I did -

Admit that I goofed and ask him for help.

Occasionally, a DH has a really good solution for a problem. (Mine will usually come through - after some grumbling - :rolleyes: )

I would buy another board, cut it in half, cover it and then staple it to fit flush with the other one. A staple or two on top of each piece to hold it to the wall won't leave any noticeable holes in the wall.

If you don't have a way to transport a complete piece of insulation board maybe you could get Home Depot/Lowes to cut it for you for a small fee so it would fit in your car.