Tool To Create Folding Plans
I had to do something similar recently.

Starting with a pencil sketch and a cutout (could be just a sketch in your case), I took a picture of it using my phone:


I imported the picture into FreeCad (yes, it is free) and used its Sketcher workbench to trace over the image. That produced a "proper" engineering model (where I could control sizes, placement of elements etc):



I then used Drawing workbench to create a technical drawing which I exported to PDF at scale, printed it out and in my case glued to cardboard to cut the final box out of:



Now, I must warn you that the learning curve of FreeCad is pretty steep, but I think it is a great tool to keep in your toolbox.