Low posterior mid placenta

This is my first pregnancy and just went for my 20w detailed scan. Doc told me i have low posterior mid placenta but told me its very common and still normal for 20w and nothing to be worried about. Saying itll move up as baby grows. Altho docs says nothing to worry or do about it. Is it normal for 20w and do any mummies placenta move up afterwards and had normal delivery? Just need some reassurance as im the type that always overthink over the smallest things (‘: