Look at your original block. Do you see the triangle that is formed by 3 white pieces? That is a much larger triangle than the one on your new block. Remember that a triangle has 2 equal sides and 1 longer side (the hypotenuse). You probably want the 2 equal sides to be straight-of-grain and the hypotenuse to be the bias.
Probably the easiest thing to do is to draw the block on graph paper. Draw the center square first, then extend lines until you can measure outside dimensions the size you need.
There are two different things you can do. The first, which is the easiest, is to cut 4 triangles per block of the needed size. Sew on two, then sew on the other two and cut off the excess white fabric. For this method, you would want to cut the triangles so that the 2 shorter sides of the triangle are about an inch bigger than your graph paper measurement. This allows for the seam allowance and ensures that your triangles will be big enough so that after you press (and starch, if you like), you will have plenty of leeway to square up your block to the exact size you need.
The other method is to cut two different types of pieces. If you look at your graph paper (or just look at your original block), you will see that once you outline the 2 large triangles on opposite sides, the remaining 2 pieces are a different shape. You can use your graph paper measurements to create a template for that shape, being careful to add 1/4" to each side of the template for the seam allowance. You could do the same for the large triangles, but it is easier to just cut those triangles with the 2 sides an inch longer than the graph paper, and trim down after the block is finished.
Edit: QuiltE described a 3rd method you can use. I always forget about paper piecing because I don't do it myself.