It seems to me that you just need to double everything. Here's a picture on a 1" grid. Don't forget to add 1/2 inch to everything for your two seam allowances. So, blocks 1 & 2 will be 6-1/2 x 2-1/2, block 3 will be 4-1/2 x 2-1/2 and the center will be 4-1/2 x 4-1/2.