Jamie~ It's NORMAL to not have your period yet at 13. I didn't get my period until I was nearly 14 and every girl expiraments with masturbation so your not alone.
You can't get cancer from it, and I would suggest that when you get your period and when you become interested in boys that you keep yourself aware and educated on things about sex, and protection and birth controls. So many young ladies aren't educated on things like that and end up pregnant or with an STD.
Some people start later than others. My twin started before me. If all you do is touch yourself, I do not think there will be a problem. You are mostly what people call a late bloomer.
No, you can't get cancer from it. My family has five sisters in it, and every sister got her period when she was 12 except my youngest sister, and hers didn't come until she was 14. It's just luck of the draw. Don't worry about the fingering, it will not alter when your period does or doesn't come. Don't be afraid, it will happen! Good luck and (((HUGS)))