sat 2 biology

I am from India and planning to take sat 2 biology e next week. Since barrons’s was not available in the country i have read kaplan’s twice and spark notes once. What are my chances of getting a perfect score?
And can i switch from sat e to sat m?

I cannot really tell you about how well would you do (I’m doing physics not biology for now). But yes, you can change the subject on test day (even to world history if you want). You can even add subjects, but you’ll pay extra fees for the subject(s) you add. The maximum number of subjects you can do at a time is 3.