1 bad sat subject test 2 good

if I were to get a 600 on the Bio M SAT2, and high 700s on Math II and Chemistry would the bio score hurt my admissions chances at selective schools? if I could improve my score to high 700s in bio, would that help for the colleges that don’t take score choice?

No

Waste of time and money. If the college asks for 2 subject tests, they will look at the best two. At many colleges, application packets are often prepped before they go to the AO, so the cover sheet may only list the top 2 anyway.

Regardless, the question might be moot since you have no actual scores. Relax and breathe.