You can retake and resubmit the CFA until March 1. However, I believe you need to notify USNA that you intend to resubmit so that they can "reset" whatever it takes to allow you to do so.
In terms of whether to take when you're out of shape . . . the test is pass/fail. However, poor scores that still pass can hurt you. Conversely, high scores can help. I've seen/heard no evidence that you get bonus points for "perseverance" in taking multiple times other than the points you get for the higher score. IOW, if you take once and later submit one set of higher scores, it's the same as submitting 5 sets of intermediary scores.
Note that, unlike the SAT/ACT, USNA will consider only your latest CFA scores, not your highest scores in each event from each test. Thus, if you improve in some areas but go down in others, the new scores may or may not help you.
In my sticky above, I've posted average scores for males and females. Do a practice test under test conditions. If you're near or above average, go ahead and submit. If you're well below, especially in the three USNA focus areas (see the sticky), I'd wait until you can submit a better score.