@realfrosty I think it’s normal to have those feelings after a huge life decision. But now, you have to just look forward, not backward.
Ignore the fact many people around you have never heard of Dartmouth. It’s a top college. If they looked it up, they would find that out quickly. In those situations, just share some excitement about what attracted you to it in the first place. (If they are supposedly a friend or family member) Remember those reasons yourself!!
The only way someone should react to your news, is by saying “Congratulations! You must be so excited to start the next chapter of your life!”
As you grow and mature, you will learn not to even care what people think - take a look at this thread, you will get some laughs. http://talk.collegeconfidential.com/parents-forum/926354-just-smile-and-nod-smile-and-nod-p1.html
Move on, work hard and have fun!