Yeah I'd say just fold it over, if it sticks out about 2" all round the waist then while the prefold is laid out and ready for you to put on fold the front edge over by say 4-5 inches and try putting it on as normal (with the folded piece inside), if it's then to short you can carefully pull on the fold to make it longer and if it's still sticks out try folding over more until you find the right length for your rise.
The other option is to jelly roll the waist once you have it on, this might leave you with a fairly bulky feeling waist band though. There are good videos out on youtube explaining how to jelly roll diapers, it's usually done around the legs but the same principle can be applied to a waist to reduce the height.
A final option would be to buy slightly smaller prefolds, assuming the ones you have still have plenty of room to come around your hips and be pinned then a smaller size should still fit around but wouldn't come up as high on your waist. If you are worried about not having as much absorbency doing this then you can simply add boosters in.
As with any cloth diaper everyones body is a bit different, even if you have a similar height and weight to another person a diaper may fit both of you differently it's all just experimentation, trial and error, to find what works for you.
