If your vocab is really weak, unfortunately, vocab takes up a considerable proportion of the SAT, and it is one of the most important skills that you must have to ace the SAT!
However, there’s good news. The SAT only tests within a limited range of vocab, around 3000-5000. I strongly suggest you download this core vocab list (a PDF file, see the link below), print it out, and memorize it. The bottom line is: you should be able to recognize the words on the test. Doing extra reading is also an effective way to improve your vocab. Magazines like Time and American Scientist contain good and advanced vocab. In fact, some passages on the SAT critical reading section were taken directly from these magazines. I know that memorizing vocab is extremely dry and tedious, but you can always make it fun. Make yourself some flashcards that you can carry around, pull them out at lunch when you are having you sandwich, and go through them a few times a day. There are lots of fun little vocab games and quizzes online as well. You tend to learn better with visual aids and sounds. Just google “SAT vocab” and you will find lots of free resources online.
Try to use some SAT words in your daily life, (i.e. in your English class, conversations, on your essays and assignments, etc)

Here’s the list:
http://img.sparknotes.com/content/testprep/pdf/sat.vocab.pdf

P. S. I don’t know about my GPA, but I am getting staight A’s, still waiting for my SAT results.

by the way you seem good at math! Are you Asian??? LOL just kidding. But seriously, you have the potential to get a 800 on the SAT Math. You got 700 already, that’s just 100 more to go! Math takes the shortest time to improve, unlike the writing and reading, which are actually steady accumulation of knowledge. But you have a year and a half right? Study hard in the summers!

HEY don’t trust Kenny, the guy who answered this question before me. Never ever underestimate the SAT, remember that your goal is 2200, which is about the 96th percentile, not a simple thing at all. I hate that when people just randomly answer questions, giving out bad advices and ignoring the need of the asker.

No offense but a 3.0 GPA is just mediocre.

After reading the other answers, I felt the obligation to tell you:
Remember: The one who scores perfect on a test never says it is easy!!!
Never wait till the last minute to study.
And trust me, the SAT Math is not what is seems.
Don’t be fooled. It looks ridiculously easy but it’s full of deadly traps! Though I am not the brightest kid in math, I got 95% in my grade 12 math and I am taking Calculus in second semester. You know what, when I took the SAT mock test, I only scored a 670 on math, because I made many careless mistakes. Such a shame, right? So you don’t want to end up like me, who always whine: if only I had studied more, if only I had been more careful, if only…..I could have gotten perfect. (That’s really sad!)

im a senior and i just took the sat like 2 weeks ago, so, i can say that it was fairly simple, math is so simple, all algebra pretty much, but as far as for vocab and stuff, the night before i took it i looked up 100 most common sat vocad word and i found this little game where you match the word with the definition, and trust me, when i was taking the sat i saw those words pop up everywhere, my advice, take it junior year and senior year, never just take it once, im gonna take it over in march or may, forget when it is but i get my results on the 14 so im excited to see what i got, oh and my GPA is a 3.0 or an 85, so it is pretty good, but i really woldnt sweat it that bad