When welding thin mild steel with oxy/acetylene use a #1 tip with about 1lb of pressure. Tack both ends and make tack welds about every 3" or so. Go back and make stitch welds about 1" long skiping every other spot till fully welded. This will keep things from warping. Take your time and only use enough heat to get the job done. I have gone as far as adapting syringe needles to welding tips to get a smaller flame to weld very thin metal and welding under a magnifying glass.
If it's not nailed down, it's mine.
If I can pry it loose, it's not nailed down.