This is an example of a floating border (if you have never floundered through calculations) . I.e., you have the quilt center DONE and you have the pieced BORDERs done and now have to figure that inner white border which frequently ends up a different width on top/bottom, different from width on sides. I followed instructions from Gyleen Fitzgerald, and the FIRST things she says is "put your brain on the shelf and just do what the instructions say". That is easier said than done! after I second guessed, third guessed , ..... 12 guessed, and finally rechecked my own WRONG figures, yes, if I had just followed her instructions, I would have saved a lot of anxiety. Yes, get pencil/paper, measuring tape and calculator and do what she says! This is the second floating border I've done using her technique, and it does work.
It needs another plain border, then binding, then DONE. Notice there are 2 different blocks.