The triangle you knitted appears to be a right triangle. To get a larger triangle out of two right triangles you need to set the right angles (90*)side by side. So the side that you have on the far left & far right actually need to be touching. That will create a straight line at the top and then the other sides of the triangles will create the "legs."
Try blocking it so that it is a true 90* angle and redo your pic to see if that works better.