Looks like they will hold but here are a few things that seemed to have helped me (I'm not an expert welder but I do most of my own welding and would welcome comments from other welders):
1. I find it hard to see the puddle with mig so get the right glass for your helmet, or if it's an auto dark (highly recommended), get the setting right and find a welding position that allows you to see the puddle.
2. Practice on similar materials before doing the weld on the car to get the heat and speed right. Looks like yours might have been a bit cold. If you can get it right on the bench, your chances of getting it right on the car are greatly improved.
3. Examine your practice welds for penetration by examining the back or grinding them down or cutting through a section. Turn up the heat for better penetration. (small welders get maxed out by fairly thin stock)
4. Make sure there is no binding of the wire in the hose (you can replace the core).
5. Grind around the weld areas of both new and old metal.
6. If you are using shielding gas (looks like you are) get the flow right. I use 12 psi for .023 wire on sheet metal. A flow meter is advisable but with a little trial and error, you can work it out as I do, using just the pressure gauge. (flow meters have gotten quite cheap).
Having said all this, I admit that I still get some pretty ugly welds too, just not quite as often as I used to.
Tom