AZTeri

I'm making this quilt totally off the top of my head and have run into an problem. As you can see in the attached picture, the second block - the rail fence pattern - is smaller than the first block, which is the size it is because I want to highlight the sunflowers. It is rectangular. From the picture, you can tell I need to add 3" to the sides and 1" to the bottom. What is the best way to do this? I think that I should make the rail fence pieces larger (they are 1" finished), but I don't know how to figure out how much larger to make them. Anybody?