You didn't say how you cut the triangles. If you are cutting squares and then triangles, the problem may be in the accuracy of the cuts. Then it could also be in the long bias side of the triangle. It could have stretched in the sewing. But my guess is in the initial cutting. Go back and measure to make sure they were to true size. Pin to make sure the seam is straight. Accurate cutting and piecing sure cuts down on frustration. If you cut from squares, what was the size of the square. Then how did you cut the triangle......all these can make a difference if not accurate. Did you go back and analyze all steps when the first test block didn't come out like you intended it to.