My suggestion would be to look up "Pot holder quilts. They are made of completed quilts blocks that quilted and bound before attaching them together. Following that method, I would measure each side, and one or both ends to see what size the additions need to be, then create each section separately. When they are finished, hand stitch the sections together using a small ladder stitch. If that does not interest you, you could put the sections together as far as the finished quilting, then use one of the methods to QAG them together. Whenever I have a new method, I check YouTube to see if there is any videos to watch for inspiration.