I did a quilt on that order recently. The rows are 1,3,5,7,9,11,11,11,11,9,7,5,3,1. To make it larger, make the rows:
1,3,5,7,9,11,13,13,13,13,13,11,9,7,5,3,1. You get the idea? For larger still, make the center rows:
13,15,15,15,15,15,15,13,11,9, etc. All you have to do is add more pieces to the center rows which will make the quilt longer and wider. You could also make fewer rows of the longest ones if you want it a little more square.