Jumping ahead or getting left behind?

Hey everyone!! I have been riding/jumping for around 8 years; However, lately I've been getting nervous over fences and therefore I over anticipate the fence and jump ahead of my horse (usually leaving me feeling extremely uncomfortable or have my horse refuse resulting in me ending up on the ground somewhere)! Anyway in order to fix this problem I try to sit/lean back as much as possible, but then that just causes me to be left behind!! :'( So does anyone have a solution to fix this problem? :'( So that I don't jump ahead or get left behind?