Patience, practice, skin stretching, and the scything stroke fixed my east-west jawline. I don't remember how many shaves it was to get it BBS, it was a lot, but I think it took about 60 to get it DFS.

I do the top part of my neck with the scything stroke first. Then I pull my cheek upwards and go ear to chin.

And make sure you have a stypic pencil on hand when learning the scything and guillotine strokes.