I would like to think that stitching long straight lines by hand is pretty challenging for even a seasoned professional. I think that is why they use a sewing machine but for us mere mortals on a budget, saddle stitching it is!
Coming from someone who has a belt on his to do list, I am not the best one to judge any ones work. IThe only thing I saw was the surface, maybe sanding it with a finer grit?