*edit* ooo... this post is a little long... apologies :)
You're in 8th grade (american?), I'll assume you're mature enough to sit down and cover the material you're interested in yourself. There are resources available on the internet that you can drift through until you, by some foggy way, figure out where to start.
I'll suggest checking out the "books" subforum here:
https://www.physicsforums.com/forumdisplay.php?f=21
And, if you are from an American school, then if your experience has so far been typical, your education in math and science has been atrocious (Here's hoping you had motivated teachers, but today, that's not necessarily the case...). Please, do not interpret this as meaning the material you are being taught is worthless! Ultimately, your teacher knows more than you do; by some methods, some better than others, they are honestly trying to get you to understand something. Besides, terrible things happen if you neglect school :). If you can find someone to tutor you, then all the better.
Understand that you cannot read something on math, physics, or anything useful in the world like a piece of literature. Somebody amazing made various useful things, among which are the pen and notebooks. Simply spouting something you read but don't quite understand will simply delay your understanding of whatever that something is.
I'll suggest this book to start out with math:
https://www.amazon.com/gp/product/0387967877/?tag=pfamazon01-20
There are video lectures, too. Search "MIT OCW," though at this point you may not get anything out of them. Focusing too much on the lectures could be counterproductive, until you know what in the world is going on.
I'll throw one more thing in. It's great that you're motivated! When you have covered trig, you can start something on physics... eventually, who knows? If you're on a budget, like I was (oh, how annoying book prices are!), then this book is good to purchase and work through. Derivatives and Integrals shouldn't be a problem to cover on your own in a month or two (be focused, don't just think you understand something by reading, do work yourself!). [edit for clarity: an thorough understanding of what is normally in the AP Calc curriculum can be covered in that time, not the entirety of calculus, you silly readers :P]
https://www.amazon.com/dp/0393957489/?tag=pfamazon01-20
(There is a volume 2, and an option to buy both volumes together. Check used prices.)
****Because publishers are... odd... you may rapidly collect prices for all used editions of any book here:
www.isbn.nu
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*edit* These are the books I listed (apologies...):
1 - Basic Mathematics (Serge Lang)
Material covered ranges from algebra to trigonometry, and some other topics. This is more effective than your typical american public/private/catholic school treatment. Can be found used for ~$30.
2 - Physics, Volume 1/2 (Hans C. Ohanian)
Material covered, if you purchase the occasionally found combined vol 1/2, includes everything in a 3-semester undergraduate physics sequence. Used copies usually sell for around $20 per edition, or $40 for the combined set.
3 - (I'm adding another...) Caculus (Spivak), for when you are thoroughly prepared. If you're like me, and feel like ramming your head through a brick wall in the presence of this book, go here (used at $25):
https://www.amazon.com/dp/0321495756/?tag=pfamazon01-20
I now place, for you, the very reachable target of accomplishing this in two years :D.
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Sorry if anything here is HORRIBLY MISLEADING, and correct me if I've made an error somewhere. I'm still in high school as well xD.
A final thing. On occasion, it is helpful to pick up some programming knowledge (and experience doing it!). But, it isn't healthy to ask you to spend every waking moment studying (you'll burn yourself out, etc.). Find out if there is a computer, robotics, or related club in your school, or in whatever high school you end up going to. Join that :D! Hence, I'm going to throw in two final things if you end up going the way of CS:
1 - An online lecture series on introductory CS (Check Stanford's and MIT's videos. I just found this, as well, be sure to check out it's home page: http://www1.idc.ac.il/tecs/plan.html). Often the language initially used is either Python or Java; you'll probably end up learning both.
2 - A BOOK, for when a book is desired, which may be found online by certain clever means, or else purchased used: C++ Primer Plus:
https://www.amazon.com/dp/0672326973/?tag=pfamazon01-20
*edit* I've been terribly pessimistic xD. Things are understood, or else learned, in retrospect. Do some things over if you need to; never get discouraged.
