Placenta previa

I'm 18 weeks and just had my anatomy scan. They found that I had a mild case of placenta previa. My placenta is covering my cervix by 1cm.  They said there's still a good chance that my placenta will move up and I can deliver vaginally, but if it doesn't move at least 3cm away from my cervix I will have to have a C-section. I'm totally freaked out! This is my fifth baby and I've always delivered natural.