If the center square is correct then the problem is with your add ons. You will need to remove the pieces and I think the seam allowance where you sew the triangles to the little square are too big. If you make those seams scant, the whole unit will be larger letting you then sew a normal 1/4 inch seam allowance to the enter square and have enough over lap on the white square points for your seam allowance.