I took the MCAT twice - the first time I took it completely cold and didn't even know the format of the exam (so I could still be ok with myself if I did poorly) and I ended up getting a 36R (13PS, 12VR, 11BS). I think this is because of a lack of stress associated with the "if i do bad it's because i didn't study" mentality.
When I did so well I decided to retake this past August without further studying and I ended up with a 39R (15PS, 12VR, 12BS) and felt like I could've done better. Again a HUGE part of doing so well had to do with the lack of stress. I did better the second time because I was familiar with the format I suppose.
Anyway, I decided not to apply to med school in the end and am going for a PhD starting in September. I was never set on med school and didn't even do pre-med but wanted to keep my options open in case I decided being a doctor was for me. I sincerely wish I could've given my scores to somebody who was more serious than I was about the application process. Good luck to you all and the moral of the story is that stress is a significant factor in how well you do. If you are able to be relaxed during this monster exam, you will do much better. I know it's easier said than done but being comfortable with the test will help you immensely.
As for the original post on this thread, if and only if you really feel like you can do significantly better in each section, you can retake because there is a possibility for improvement with such a lack of preparation. Prepare and go but it's definitely a risk.