King of Tokyo: Number of points/hearts
You do not have to hit 20 points exactly, you just need at least 20. While the rulebook doesn't state this explicitly, this is how pretty much every game works unless it specifically states otherwise. Getting 21 points DOES mean that you've gotten 20 points; just like how I literally do have $20 even if I also have more money than that.

The heart dial goes to 12 because certain card effects can increase your health above 10.