Dear Cordelia,
A significant percentage of the quilt patterns for sale are NOT 100% original designs. They're based on traditional (public domain) blocks, occassionally in clever settings, and named according to the author's whim. (because of the fabrics, or the colors, or the intended use of the quilt.)
This is not to imply that the pattern designers/authors are cheating their customers. They usually include fabric estimates, cutting instructions, piecing diagrams and instructions, and sometimes extra layout variations. That's often where the true value of a not 100% original design lies.
You applied your vision of fabrics, colors and arrangement to the quilt. It is therefore, uniquely yours. :P
Solve your piecing dilemna with the twisted squares-in-diamonds by using the EQ software to generate a paper-piecing foundation pattern. (if you don't want to paper piece, you will still know the order in which you should attach the pieces to each other to achieve the look you want.) if the odd angles make rotary cutting complicated, use the EQ again to generate templates. you don't have to use them to fussy-cut individual patches for the block. print them on freezer paper and iron them to your strips to use as cutting guides.
The only remaining step is to have more faith in yourself. You CAN do it. :P