SAT/SUBJECT TEST PREP ADVICE??

Hi!
Im a junior and Im realllllllyyyy scared for the SAT and math 2, biology, and chemistry subject tests. They completely changed the SAT this year and I’m scareddddd! I want to go to an international college and literally the only thing they look at are these four tests. I really have to do very well on them, this college is my dream! How can I get 800s in the three subject tests? Also, how can i get a 1560+/1600 on the SAT?? Are prep courses worth it?? Please help mere

meee