I would rethink it entirely and use the extra squares for either shams or throw pillows. that way, any issues with seams and durability will be less. Then, I'd keep the quilt as is, coming up to where the pillows stop. You can buy coordinating solid sheets and cuff the edge over the top if the quilt edge. This is easier on the quilt, as it's not folded and edges aren't being rubbed together all the time. And looks good, IMO. Stores display bedding like that all the time.
hugs,
Charlotte the outlier