Ross, I don't think that weld bead looks bad at all. Tig welding a small bung on a big hunk of alum is a challenge for starters, and you don't want it cracking, breaking off or leaking. I used to do lots of Tig welding, and my boss impressed on me not to make "tiny welds" as he called them. Idea being a small bead can equal a weak weld joint that could give you problems down the road.
Bruce