Hi Elisabeth, welcome to Scrap Girls and thanks for purchasing my Curvy Mats. So you want to know my secrets?
I'd create a custom shape to the biggest size I'd want to use it at then rasterize it. (Elements people, help me out here, please.) I'd make TWO duplicates of the layer (so you have three layers). The I'd use my magic wand (set at contiguous) and select the outer border and delete it, on layer #2 I'd select the center part and delete it and on the last layer, I'd select the space in between the two parts. Then I'd add a blank layer, and fill using the paint tool. I'd then add styles to each and go from there. Hope that helps, I'm typing fast because my dogs are hungry, lol--dinner comes before scrapping in their tiny world. Let me know if you have more questions, someone here can help, or I'll get back to you tomorrow afternoon.
OK, that makes sense...off to play a bit, thanks so much!!