The August 2019. SAT math curve was quite harsh. That alone shouldn’t make a big difference between SAT composite score taken at different test dates. Since this was your first official SAT, maybe you are not quite at the 1500’s score yet. Since you are a Junior, I would hold of on taking another and focus on the PSAT first. If you are truly a 1500’s scorer, you should do well on the PSAT and it counts for you this year.
As for top tier school super scoring, you can look up each of the school, they have their policy.