SAT II sending less than recommended

Hi. I am interested in applying to a selective school that recommends 2 sat subject tests. I would only have time to take the May subject tests. I have been reviewing for the Biology, but I don’t feel that I could adequately prepare the math in time to get a high score. Would I be better off sending just one subject test and doing well on it or sending a math and biology but have scores that may be less than average? Thank you:)