Don't give up hope bro!!! GPA and MCAT are just two among many parts of the deal. Imagine that you are a member of the adcom who has to review hundreds of applications, most of which come with more or less equally high scores (most have 38, 40 MCAT for example), then you might find that in this case those high scores are not as impressive any more! So instead you (the ad com member) would go for the application that impresses you the most - the most moving story, the nicest LORs, the activities that portrait the most passion etc.
So instead of worrying about your stats, let's think positively (as you rightly mentioned above): if your stats are bad and you got interview invitation, that means your EC and LORs and other things must be not only very impressive but also somehow unique! Be proud of them, and think about them while you prepare yourself for the interview - how do your activities tell you about yourself? what have you done that make your profs/boss praise you so highly in the LOR? Know yourself, especially what makes you unique, and you should be a fine applicant regardless of your scores.
