What you did was dangerous, there are Darwin Awards for just this type of thing! The likelihood of something going wrong is low, but the consequences are terrible if it does. There are many failure modes when jacking up a car: Scissor jacks are pretty reliable but they can fail, the ground could be unstable or the surface could collapse due to the weight. I've had a jack point collapse due to hidden corrosion one time, went right through the body of the car that looked completely solid!
Even if nothing physically fails a jack can slip if it's not positioned right, say it's off center from where it should be, kicking the tire may move the car just enough to bring the car down.
I keep a lump hammer (a short handled hammer with a big, heavy head) in my trunk just for this type of event, but there are a few tricks you can try if you don't have one:
- Loosen the nuts on the wheel a bit then drive the car forward and backward slowly, you can try driving slowly into a kerb as well
- Hitting the tire with the tire iron over and over. It doesn't sound like much but it works remarkably often
- Hitting the outside edge of the tire with the heel of your hand over and over. Again, it doesn't sound like much but I've had good success
- Although it's already been mentioned kicking the tire works well, and would be the first thing to try, obviously not from underneath the car. Kicking the outer edge of the tire gives the most leverage as it's farthest from the hub. Lying flat on your back and kicking with your heel gives you a lot of power, if the tire comes off it may fall on your legs though. Kicking while standing is not something I'd recommend if you're close to traffic as losing your balance may cause you to stumble into the road, which is bad™