Chill. As long as your GPA's are fine, then these grades won't keep you out of top 20. As Ace has pointed out, it's fine to aim high, but don't be so set on 'top 20'.. You'll just stress yourself to death. And getting into those top schools requires much more than good grades, so do keep that in mind. You won't truly know if it's possible or not until you apply. For now just do the best you can.