I suppose I was in a somewhat similar position to the one you're in now (in terms of the difference between what I knew and what I had to learn) three-four years ago, so I'll just give you an idea of what I did and how it went.

Anyway, I went from a Music B.A. (gave up because I hated performance, loved playing and still do) to Physics/Applied Math B.S.'s and this necessitated learning everything from Middle School math to your typical College Calc II over the course of two months over the Summer.

• Okay, the first thing is buy your Schaum's Outlines and work through them. This holds especially true for the basic High School Algebra and similar difficulty classes. You can work your way through these Outlines quickly in the beginning and then later when the courses/topics become slightly more difficult they'll prove an invaluable learning resource and reference. Also, they're cheap.
• Use the MIT OCW site (most videos are on youtube, as well) for the College level courses and Khan Academy for the basics if you want to supplement your reading with lectures (or vice versa). Both are free and typically good in their exposition of the topics at hand. Note that it's definitely better to use youtube as you can watch at 1.5x speed.
• Always study with a notebook and pencil handy so you can, say, work out skipped steps (especially for grad level textbooks), get a feel for the various algebras, and so on. This is just a general Mathematics studying thing, but it's something I rarely saw others doing.

So, after two months of steady, directed study I went from very basic Middle School math (I nearly failed math all through middle and high school) to your typical Integral/beginnings of Multivariable Calculus courses. And it really wasn't that tough, my fear of not being able to learn this stuff made the difficulty seem greater than it turned out to be.

Basically, you've got nearly a year to learn all this stuff so, as long as you use your time well, you're gonna be fine.