What you can do is cut freezer paper to the finished block size and iron that to the back of your t-shirt pieces. This will stabilize the edges when you sew. Pin and sew your seams right up to the edge of the freezer paper. Peel off freezer paper afterwards.
The blocks on-point have stretched along their bias sides. That is why you are getting the ripples in the point ends.
Edit: I mean adding the freezer paper to your already-interfaced t-shirt pieces.