[BR3W CITY]

Cougar, here's my .02 on the weld I see:

It looks like your trying to go for the overlapped "bead" aka the Mig-like-tig weld. Totally fine to do, but on thin sheetmetal (like a truck repair) it doesn't really teach normal welding technique. As you overlap those little beads, your keeping a lot of heat in one area creating a higher chance of warpage.

Try spacing your tac's out an inch or so and keep your fitment tight. On a sheet repair you'd hammer and grind the seam, and then come back for another round of tac's and small welds, planish, repeat.

To improve your general welding, get yourself some thicker material to practice on. Thicker stuff can be a bit more forgiving on heat, and you can get a better (longer) time with the puddle to observe its patterns. As I mentioned above, the technique on the thin stuff is pretty different than "structural" welding for lack of a better term.

Pickup some scrap 1/16, 1/8, 1/4 flat and/or some sch40 and 80 black pipes. With that stuff, watching videos from Jody @ WeldingTipsAndTricks, and setting up your scrap in the basic 1g,2g etc etc positions, you can progress through most of the basic fitments and weldments, and it'll give you a really solid base for any fab you want to attempt in the future.