Not bad for a first try, Drew. Reminds me of a summer job tryout where I was supposed to stick weld garbage dumpsters. Spend most of the morning filling holes, and was told not to come back after lunch! :laughing:
That finished weld on the right does show that you're getting the hang of it. It is very difficult to stick weld cracks on thin sheet like that, so you're trying to learn on a job that challenges even experts. Minimum thickness to weld easily is 1/8" in my experience. I don't know if that application would allow it, but you could put a steel backing strip underneath the weld on the left and it would make repairing the crack much easier. Harbor Freight makes something they call a weld spoon that is supposed to serve the same purpose but not become part of the weld. Looks like it might work, but I've never used one.
What diameter of electrode are you using? Try 1/16" if you haven't already.
The problem is that once the weld pool gets too large, surface tension can no longer hold it in place and you get a hole. The trick is to get the arc going, create the pool, then pull the electrode away from the work to decrease the heat and let the pool shrink and solidify, then move forward a tiny bit and lower the electrode back down put more metal into the pool. Repeat that to stitch your way along the weld. It takes practice to pull back enough to drop the heat without letting the arc go out. If you don't want to move up, you can also move forward along the seam away from the pool, let it solidify, then move back onto it to create another overlapping pool.
Here's a pretty good summary of stick welding technique, along with a thickness chart at the bottom.
Arc Welding aka Shielded metal arc Welding
And here's a little calculator that'll help you set the welding current and pick a good electrode:
Stick Welding Calculator - MillerWelds
Thin sheet like that is where MIG welding really shines because it's so easy to start the weld, make a pool, then just let go of the trigger to let it solidify. Move forward a bit, pull the trigger, and repeat so you end up with a series of overlapping spots.