Well, in some ways you are not ready! The bottom line is that your first two months, people will constantly reference authors you have never read, ideas you are only vaguely familiar with, and theories you have only briefly studied as an undergrad. I understand your anxiety, but you are not as great as you think you are right now, but you will grow as a thinker in graduate school and it's obvious that you have what it takes to take on this development. If you go in thinking that graduate school is going to be an extension of your undergraduate career then, forget about it. You'll do well. In the end, graduate committees (at least in the humanities) look for students that are willing to learn and grapple with new ideas and they obviously saw that in your application.