When you take does not matter. If you're nervous about it, then take it in October. This will give you the opportunity for a retake in November. Only a few applications are due before the December hear-back date for the November test, so no worries there. But ETS is annoying in that the sign-up date for November is a few days before the October test, so if you need it just in-case, you have to spend tons of money (and to get your October score before the November test, you have to spend an extra $12 or something getting the score early by phone).
Anyway, the CS will be pretty much irrelevant both for the test and your applications' success. There may be one easy GRE question asking you to follow some algorithm they give you the pseudocode for. For applications, your CS stuff will just basically be an extra line on your resume unless it has significantly impacted your mathematical interests as indicated on your personal statement or your recs, etc.
As for the content of the GRE, there will be a few questions on topology and complex analysis, but trying to rush through that stuff just for the test just isn't worth it IMO. The biggest worry I'd have is your missing real analysis. There are several questions that will be very difficult if you only know the computational stuff (calculus). There's just no way around not knowing analysis well. You'll need it for the GRE, for grad school courses, and you'll need it for the analysis qual obviously. Nevertheless, about half of the test is just speed Calculus, so the number one priority is being very comfortable with Calculus. There's no substitute for working lots of problems (TAing Calculus for two years helped me a lot). There will also be a couple questions on DEs, so focus on that in the fall.
Some schools might expect you to have more courses under your belt, but if you can manage a competitive score on the GRE, then they might not hold that against you.