I think you did well by cutting the leg to the desired angle first. That'd be the way I do it, too.
Does this sketch describe your situation (invert the diagram since your leg points downward)? If so, mill the post at right angle, and mill the leg also at right angle to the endgrain:
If you provide a sketch or photo showing the dimensions of the post and leg and how the joint looks like (i.e. how the mortises are oriented), the mortising advice could be different.
