All schools will accept MCATs of September 19th, as that is the last exam of the year. However, these dates are more designed for people applying the following year. If you take the 9/19 test, you get your score back 10/23. If you apply then, you might need 1-2 weeks to get verified. Then 1-4 weeks before you receive any secondarys. Then it may take a month or more before each school reviews your packet. At this point, many schools have already filled a big portion of their incoming class, and most of the interview slots have been filled already. The only people that get in when applying late are high stats folks. If you have already have a low first MCAT, then it will take a really high second MCAT to make this group (probably like a 520).
If you are not feeling ready now, then stop. Take more time, and do the MCAT right, then apply in 2019 for matriculation in 2020. A second bad MCAT, especially so soon after the first, will really hurt any chances. Take a gap year and use it to better your application.