I have a pink and white version of that on the wall in front of me as I type
. Thanks to Iminie being my partner in the Christmas exchange two years ago!
I agree with Imi, the African print is lovely, but it's too strong to go with those lovely pale pinks.
I would make a wide pieced border separated from the pinwheels with white sashing (which you already have) another white sashing and then a pink binding. Choose a different block for the border, but one which complements the pinwheels
21x27 ->50x60 means adding 29/33 inches, or about 15 inches all around which is quite a lot for a border. Maybe two pieced borders (6 inch blocks).