When you're applying, you're competing, not with yourself, with others. You get interviews because you're competitive and show promise based on your scores, activities, personal statement, and letters.
You also need to realize something, not everyone who gets an acceptances attends that school. For the admissions committee, sending out an acceptance is a gamble because there is no guarantee the student will even attend their school. Plus, prospective applicants that were interviewed are often interviewed at other schools as well. This means many schools will often overlap on the students they interview. They often interview 5 times the number of slots they have because there is a good chance many of the applicants they accept will choose another school. The average matriculation rate for MD is about 40%. I say maybe the top 50-60% get interviewed, so your odds are 2/3 just don't blow it. Also, if you can get interviewed with at least 3 schools, you're probably in. Plus, in rare cases, some defer admissions as well.
Keep in mind they would not interview you if they did not see potential in you. Just be yourself and assuming you are not lying on any of your application material, you're probably in.