That sounds about right. ^
I did my creeper gussets, top gusset and undershave job on my front axle the same way and still ended up with i think a hair of warpage.

Its kinda... ghetto, but you can always burn a couple real hot beads on the underside to counteract the warpage on top.
It wont get it perfect, but it can bring it back into shape if its really bad.