are you quilting it yourself?
because if it is going on a frame you need to add 8" to the width and to the length.(4" more on each side) .so the quilter has enough to attach it it to the frame..
and it is certainly not s stupid question at all..
how much of the sunflower fabric do you have left from the front?
This shows you one way to piece the back..she used 3 different fabrics..
http://www.jaybirdquilts.com/2011/05...uilt-back.html