I got two B's second semester junior year of high school. How much does that ruin my chances of getting into a good school?

For UCs, particularly now they are test blind, Bs do matter and your grade trajectory is down not up. You’ll be evaluated in part against others who have applied from your high school in the past. For my daughter’s high school, admits had a gpa avg of 4.21 for Berkeley and 4.27 for UCLA. You can find that here: