<p>Was it nervousness? Too much time on one problem? As long as you work quickly (don’t spend too much time on one problem unless you’ve solved everything else) and don’t mistakes, you’ll score an 800.</p>
<p>It sounds to me like you’re not timing your tests at home. It is very unlikely that you can score 800 at home, and then only get a 600 on the actual SAT, unless you had an exceptionally bad day. You need to get an accurate score for yourself using an actual timed College Board SAT so you can be realistic about where you are, and you know how to proceed. After you have an accurate score, then look at some of my articles such as “The Correct Way to Prepare For SAT Math.” If you are in fact getting at least 650 on a timed test, then you can read my article"The Correct Way to Take the SAT for an 800 in Math." Most of my articles are posted on this forum. Just do a search.</p>
<p>Haha, there are so many (official) practice tests that are posted on CollegeConfidential (let me know if you can’t find them). I would say to do timed practice (like DrSteve said). And look at solutions and review the questions you got wrong. In addition, for questions you got right, but took a long time, look at those solutions too and see their approach. Best of luck!</p>