Im not an expert
The bulge is because as the welds shrink they also pull parallel to your seem
This means extra metal in the middle as the edges get shorter
It might go away when you expand your welded seems ever so gently
Im not sure if this bulge can be set aside until you are done all welds or if you should do an intermediate remedy.
Personally I would attempt at slowly finishing the weld as long as I only see a bulge and not full on waves because there is just so much extra metal it can’t fit in one curve
Then I would tackle the bulge
suggest you watch a few videos on how to shrink sheet metal
You will need a torch and a wet rag
Figuring out where to try to shrink it just right is the skill part
I usually am not aiming for perfection
So let’s collect more forum feedback don’t run off and do what I say
That might make it worse
-s
