newbie here need some help please

In a bit of a panic here, I am in the army and have my upcoming annual fitness test in mid jan, and for the life of me I cant do the required crunch, I don't know why but I have always struggled with this test, I'm not fat, I run a lot so fairly fit.The problem is I cant bring my hands far enough over my knees, nearly have to bounce off the mat to get them over the knee and that is not allowed. I don't know maybe if its just that I have a weak back or core, or short arms http://www.physiobob.com/forum/images/icons/icon10.png I was considering starting pilates ,would that help? anyway I'll attach a pic of the required crunch, If i don't pass this test I wont be deploying overseas in may. Thanks so much if you can help.