I *think* that one of the triangles is not big enough. Couldn't tell you which one though.
You need dog ears showing at both ends, that's your seam allowance to make sure the point is in the right place in the finished layout.
You have what looks to be the right seam allowance at one end, and none at the other, so you are missing an entire seam allowance in your measurement.
Cut another square a 1/4 inch bigger, and try again. Maybe do it with some scrap fabric first till you're confident it's right.
Good luck! :-)