Low placenta

Claire
I'm 33 weeks, on Thursday I have a scan (34 weeks) to find out if the placenta is still low as it was on my 20 week scan. This will determine if I need a c section or not. I'm really hoping I don't as I really want the experience of a natural birth but I know it's ultimately what's best if they do decide I need a section. 
Anyone else been told their placenta was low early on and then it moved in time? 
If you had to have a section how quickly was it booked in?