Looking good, keep on trucking. A bit of unsolicited advice that has really helped me welding sheet metal. Not critiquing your work man, just trying to help if I can. These are some of the "learn as you go" skills I learned so far in my project. You can almost see as you look at my project the exact point in time where I picked these up.
First, cut about an inch into the good metal (when possible) when cutting the cancer out, it gives you good metal to work with.
Second, make the patch piece fit as close to perfect as possible. This helps you from generating too much heat trying to bridge the gap. A small gap < the thickness of your mig wire is ok. You are using .23 wire right?
Then clean BOTH sides of the patch and original at least an inch in on both pieces (again as long as space permits), this makes for a better electrical connection for your weld and removes contamination. It takes a little longer to do this but it really helps reduce burn troughs and makes for a better weld.
Hold your trigger on your welder until you hear that really good consistent sizzle (not the pop, pop, pop sound). That lets you know you have a good electrical connection and that the metal is getting hot enough to melt the mig wire and both pieces together (penetration). That's just a second or two.
Lastly skip around to minimize heat distortion. When skipping around you will notice that the welds get a black sut on them. I use a small wire brush and clean them off before I go back over them. It helps me to see where I need the next spot weld so I don't leave gaps.
And then grinding. That's a another deal all by itself. If you want my technique for that let me know. I'm a little uncomfortable giving out this much unsolicited advice and don't want to make anyone upset.
You are going to have a sweet ride when you are done!
Steve