Equalateral triangles have bias edges that stretch if not handled carefully and sewn exactly. I starch my fabrics, pin and mark the 1/4 inch mark at the point to stop sewing at the mark. It looks like you will have to pick out your stitching, starch your fabrics, remeasure the pieces, mark your 1/4 inch seam allowance and try again. Good luck and this is one if the trickier quilting shapes so pat yourself on the back when you get it right.