Difference between 3.7 and 4.0 GPA in the eyes of colleges?

I thought I had a 4.0 GPA because I've never earned a grade lower than a 90 in any of my high school classes. It turns out, however, that on the unweighted GPA scale my GPA is actually a 3.7 (according to my guidance counselor). I've taken the most difficult classes throughout high school, and I'm hoping to attend a highly selective college. Will this slightly lower GPA damage my chances?

No, a 3.7 unweighted GPA is not going to damage your chances at selective colleges if you've taken the highest-level classes available to you at your high school. As long as your test scores are also good, you will have a solid chance of acceptance at virtually any school in the country.