Sorry but that is not a right angle (considerably less in fact), even if it was drawn accurately.
Well, it's no good saying that it would be "considerably less in fact" if you don't know what it is exactly. But you are right, it is not a right angle. If you want accuracy, you should divide that triangle into two. Apply Pythagoras theorem twice and add the two answers. I bet you, you'd get 171.8nm.
Btw, if drawn properly that angle would be 89.8 degrees.
