Is giving birth early or later hereditary?

So my family of females has always given birth early. My mom was born early I don't know how early and I was born 3 weeks early. And my great grandma and so forth from what I know were all born early. What are the chances that my baby will be born early? I walk ALOT I am walking over 7 miles a day. I hate driving so if I wanna go somewhere I just use my feet. Save gas save money pretty much is my thinking. So with all my walking my family keeps saying how great my labor will be because all I do is walk that my lil guy will pop right out. Well lately I've felt a few braxton hicks contractions but they come once then disappear for days. I'm only 23 weeks pregnant tho. So does it sound like I'm going to be early??? I panic because I'm giving birth alone (I'm sorry but there is no way anyone is gonna see what's going on down there besides my doctors and me. My husbands deployed.) and I wanted to get things ready just a few weeks prior to my due date but I'm worried I may be to much earlier and wont be prepared. Advice?