I agree with Kevin, your pieces don’t appear to be clean enough for good strong welds. The edges need to be ground to good solid metal, free of rust and paint (front and back), otherwise the weld is going to draw the contamination into the weld giving you porosity and a weak weld. It will be much easier to weld, your welds will look much better, you’ll get less spatter and it will be a much stronger joint.
Just don’t get carried away and thin the metal too much. Keep at it and you’ll get it!
