I have been sewing and quilting for years and years and I still struggle with 1/4" seams. I just bought a quarter inch foot for my machine that has a metal bar on it so that the fabric doesn't shift past the bar. I think it helps. As for your block it really sounds as if the pieces don't have the 1/4" seam allowance added to it. That's the only thing I could think of that would make that big a difference.