How bad is indoor tanning?

I did indoor tanning for two years on and off, from about beginning of '07 to the middle of '09. Some weeks I would go very frequently (like 3x). I know it was bad for me, but I liked getting color. Growing up I never really had any bad sunburns and always wore sunblock. Now I'm just afraid that I will develop melanoma at some point. My grandfather (now deceased, not due to skin cancer) had small skin cancer polyps show up on his face in his 70's and 80's but he said he spent a LOT of time in the sun throughout childhood and young adulthood. My parents don't have skin cancer (at least not yet). I have brown hair/brown eyes, and burn first and then tan. Sometimes I still go to the booths, but like once every few months or so when I get a coupon or something. I know it's stupid, should I be really scared?