Stretch Marks??

I'm 28 weeks now and have no stretch marks yet, what are the chances that I will still get them or should I be good? Someone told me they're genetic but I really hope not because my biological mother had terrible stretch marks that still look terrible 20+ years later. I also have a burn scar on my pelvic area, off to the side, it's low enough that my underwear cover it, will that stretch? I worry because certain movements pull it and it's very painful and it scares me that my belly might eventually pull tight enough that it's going to pull the scar.