You want to separate the dark and light pink, back to about 1" before the dark pink reaches the dark pink in the side border. Also separate the dark & light pink on the side borders...back for about 2".
Stitch the dark pink sashing on the top as usual, ending at the end of the dark pink in the side border.
Now, press the seams & reattach the light pink to the top dark pink sashing, and also reattach the dark pink side sashing to the light pink border...finish off the stitching to finish the borders.
Takes extra time, but can be done.
Marge