PSAT question?

Can you take the PSAT twice? Because I really want to take it in sophmore year, but I also want to take it in junior year to try for the National Merit Scholarship. But I also want time to be able to retake my SATs, so I don't want to take them senior year. Can I take like, the PSAT sophmore year, then in the begginging of junior year take the SAT, keep retaking it until i get the score I want, and on top of that take the PSAT in the last semester of junior year to get a chance at the national merit scholarship? Suggestions?