You're probably better off putting this in the TA forum rather than the Fitness one. However, it's not a case of failing, just a case of "go away and come back in six months once you've addressed these problems".
You seem a bit nervous about the whole affair. Confidence is an important thing in the military. My advice would be to just give it your all on the day. If you do well, job done, if not just chalk it up to experience and go back once you've got yourself in shape.