This is a pretty common feeling amongst medical students, (and plenty of other people going to uni as well). You're used to being a big fish in a small pool - most med students were at or near the top of the class in school. And now you're with a load of other people who are at or above your level and it can be quite an adjustment.
That said, don't go the other way and put yourself down. You didn't get 'one lucky offer', and you shouldn't minimise the importance of hard work; it will get you much further than mere intelligence
Words of wisdom? Remember that if you're the smartest person in the room, you're in the wrong room. You meet a lot of interesting at impressive individuals at uni. Instead of feeling intimidated and inadequate, choose instead to learn from others and be happy and proud of their successes. You'll probably find that they're not geniuses, but just pretty regular people with some good exam results. Some of them may even be intimidated by YOU!