Hi Mendel, I wouldn't worry too much about the pointy corners if this is your first build. You have the Titian poster right? So on your next build, copy the corner blocs from the CT scan on the poster. The shape of the corner blocks is what makes the corners. Blocks too long = corners too long. Make mistakes on the first one, correct them on the second build.
Make templates from the poster from the back plate CT scan since it will be less distorted. Use half templates. Well that's what I do anyway. I'm a beginner too, not an expert, so just my suggestions.