You can check on the web site where you completed your supplemental application. Log in with the same password that you were given initially; under the admissions tab there is a link for required letters and credits. Just make sure that you don't have any items not marked as recieved (with a date). If any thing has a red X or a green check mark, you'll need to follow up. Later you can check your admissions status. It won't show accepted until you return the matriculation agreement, but it will show either that they have made a decision on your application (translates to accepted or rejected) or that they are still reviewing your application (waitlisted) about a week to 10 days after your interview.
I'm not sure how many seats are still open, but they are still interviewing for a reason. Many of the applicants who were accepted early in the cycle made a deposit to hold a seat until they heard from other schools. I would expect that many seats that are already filled will open up again before the fall. Stay positive! It's a nice school, I'm sure you'll enjoy the visit... although I did find the large desplay of ceramic clowns upstairs rather disturbing. LOL