First and foremost, that quilt is incredible. I've yet to do a T-Shirt quilt, it is something I would like to do for my nephew at some point in time.
That said, I'm going to follow this thread because I've never had this problem, either and I am interested in seeing what others may suggest. My gut would tell me to pull the binding off the bottom like you're thinking and maybe trimming it in the middle where that extra inch is, that might be where the problem is but I would have done the same thing and asked for advice before I did it.
Again, the quilt is incredible, fantastic job!