Twins

Hi so I am 29 will be 30 in September and my fiance and I are getting married in 2 months. I'm a twin and I have an older brother and sister that are twins. I want to get pregnant by the time I'm 31 but I'm terrified of having twins!!! I don't have any children and have never been pregnant before so I'm just super super nervous about having kids. Any other people out here feel like I do? Do I really have that much of a chance of getting pregnant with twins?