Reschedule to January if you truly think that will help you. Theoretically, more time should help, but consistent studying for the next several months will be easier said than done. If you look around here and the reddit mcat page you'll see people harp on how important it is to review passages the right way. I like 7sage's approach to reviewing lsat passages because it can also help you review mcat passages and because it incorporates timing and analysis of right and wrong answers, really allowing you to zero in on issues with your content knowledge or thought process. This method takes a lot longer to review practice passages with but can only help. Once you are consistently getting high percentages using this method then is the time to transition into practice exams, which this method can also be applied to. Once you are getting scores in your target range on these exams, then is the time to schedule your mcat. I honesty wouldn't even schedule a date for the exam if I were you. I would wait until you are ready to take it and then schedule. Seats will open up closer to test dates as people drop them.
So I've been studying since the middle of June using TBR content and their passages. I've also done some EK 30 min exams, but haven't been doing so great. The TBR passages have been quite rough, and I haven't been improving much at all. I've taken two half lengths from NS and Altius (got 503 and 497 respectively..), and I've taken EK FL 1 and only got 60% overall (64% CP/51% Cars/64% B/B/61% P/S).
I'm signed up for a Sept MCAT date and am considering cancelling and taking it maybe in Jan 2018 since I do not really feel ready and feel like I'm rushing at this point. I'm not quite sure how to really improve my studying or passage based practice as I feel like reviewing content has been okay, but when I get to practicing, I just can't understand the passage or my reasoning is just plain wrong.
So I was wondering if I should just cancel at this point and take it at a later time.
I agree with the other poster, you shouldn't take it until you feel ready, and you really don't need to schedule right now either. If you're applying next cycle you have tons of possible dates to take it once or even do a retake and still apply early.
That said, I think a lot of people make the mistake that more time = a better MCAT. I've also seen some people just keep pushing it back because they're intimidated by it and can, but ultimately find themselves taking it when content isn't really fresh in their minds. I
m not implying this is your case but it's something to think about.
Were it me, I would take an AAMC FL and see how you do. If it's significantly lower than what you're shooting for, than I would reschedule. AAMC FLs are by far the most indicative of the real thing and give a pretty solid range of where you likely will ultimately score.
Do you guys have any recommendations on source material? The prep books I have are TBR and EK and was wondering if this was sufficient? I'm hoping to get at least 515 and I'm not sure if I'm ready to get that type of score yet.