Flatten some copper pipe and hold it to the back of the panel to draw away heat and help stop you blowing holes, just like using a copper spoon to weld in patches to a car with a slight gap between panels for full penetration
That's probably the way I would have gone about it myself, good job. You could take a die grinder and tart the weld up more but if it's being hidden away it's probably not worth the ball ache
I spy a CB750 fuel tank there.