Joss - measurement of fundal height is extremely inaccurate.
I understand you have a past history to take into account but it is vital to remember that all women and all pregnancies are different!

Think of early dating scans - they are best done prior to ten weeks because until then most foetuses develop at the same rate - past then they grow differently.

Scans, measurements, etc - they tell us nothing about the babies size. In an ultrasound to try and detect size of bub - they measure the femur (I think) How does measuring a leg bone tell us the weight of a person - a baby no less. Maybe you have a tall baby!

YOUR body will not make a baby that YOU cannot birth. Have faith in yourself!