I would suggest as Kitsie says and try with paper first. I think you're just having an issue with how you are positioning your triangles - provided they've been cut to the correct size. As in the diagram you provided, you'll lay out your row of blocks and then take the triangles and just keep rotating them until you get the right angles (what are actually the 'points' or 'centers' of your cut triangles facing the bottom left/right sides of the blocks. Hope that makes sense for you. Setting triangles can be a bugger to figure out sometimes!