I have a hard dime size lump /ball I'm my cheek by my chin?

I had those before. I'm not sure what it's called, but if you leave it alone, it goes away. It's tempting to touch it, but the more you do, the longer it stays.
It's usually caused by too much pressure of the jaw, so don't clench your teeth hard or something of that sort.
If you're still worried, go see a doctor to make sure it isn't harmful.