I thought it might be helpful to start a new day with a new thread! To achieve a rectangle of 1" x 2" finished:
Having seen the pictures, I have now drawn out the triangles in question. The centre larger triangle, when the seam allowances have been added on, should measure 3 1/8" along the base and 2 1/4" on each side.
Each of the smaller triangles should measure 2 5/8" along the base and 1
7/8" along each side.You can now see the first part of your 'problem' - it looks to you as if you are joining a 2 5/8" raw edge to a 2 1/4" raw edge. But this discrepancy is only at the outer edge, the raw edge.
However, the raw edges are *NOT* what you should be matching. Within those two longer measurements are the *sewing* lines, and these are of course equal at 1 3/8". These are the lines you should be matching. As you have now got confused and 'fed-up', just draw these lines in (on wrong side of fabric) on the next one you try. Match the *sewing* lines and ignore the raw edges completely (pin corner to corner).
When joining triangles, never try to match the outside edges of the pieces. Anne suggested placing dots at the ends of the sewing lines. Do this after having done one with the full lines drawn in. Then you can just manage with the dots thereafter.