Millermatic 200

You are gaining experence real fast.
Run 75/25 gas.
.030 is not a bad wire to weld sheet metal with.
Looks like you need to move faster, your beads are way too thick to prevent sheet metal warpage.
You have to spot weld sheet metal, and even then it will bow in and out with out support on the other side.
Brass is your friend, weld will not stick to it.