SAT registration

It doesn't make any sense to register for a third exam when you haven't even taken a real exam yet. If anything maybe sign up for the ACT because sometimes people do better on the exam they didn't choose because there's less pressure. But if you truly study hard and take practice tests, you should need only 1-2 tests. There's a huge drop off in returns once you get to the third exam and you're usually better served spending your time on other things. Especially if you're at least average for your school.

This heavily depends on what colleges you want to get into if Ivy League is you goal I’d say taking additional testing is a decent idea but if you are going for regular state schools like Oregon Kansas or Maryland you are in great shape. And if the schools you are interested in do superstore you should be done and don’t need additional tests and average sat at elite public schools is around a high 1300 Virgina a public ivys average sat is 1350 so you should be fine.

Taking the SAT more than 3 times is not a good thing, college administrations see it as an unsure and weird thing to do and they start to questions your school's education. Take it 3 times MAX and use the highest score of them. Practices for SATs are available in collegevine and Khan Academy to improve your score.