There's no real way to completely diagnose this over the internet. You have to be aware of all the realities of your own sequence. No doubt, this was a good learning experience, especially seeing that you can heat the sides of the tubes to induce a bend in them (though it's a bit misguided).

Take the time to consider the warpage of your BB shell and how it relates to your alignment check. Get out your caliper and measure across the top of your BB shell and then at the bottom...note the difference. Do this after you tack and then again after your fully braze the DT and the ST to the shell. Note the difference. If you're using an alignment system that relies on the face of the BB shell as a datum, and that datum is no longer parallel to the centerline of your frame, can it be trusted?

Your front end might not be as bad as you thought it was...the point is that while it's great that you're self-critiquing your brazing process, don't neglect the alignment aspect of it, the tools, what surfaces you're using to read alignment and how heat has affected them. Did you buy that table or make it? Have you verified that the face is parallel to the table itself? I ask because I've seen a brand new $8K Marchetti table with the face of the whipping post 0.004" higher on the bottom than the top which prompted the owner to chase his tail for months wondering why no frame checked on the table appeared to be straight.