I'll reiterate my endorsement of Sarah Cleveland, and I also like my fed courts class with Monaghan... I will warn say, though, that Monaghan can be a little crabby and, as one of the leading Federal Courts scholars EVER, he teaches to a level that most of us don't understand until a few days after the lecture. To an admit, the class might just be a confusing blur with an old crotchety guy telling everyone they're wrong.
Also, in any large section (i.e. any 1L class), you just walk in, sit in the back and leave. If a professor does ask about you (which I HIGHLY doubt will happen), don't worry about it. Just say... ohh... uhh... I'm an admit. If anything, they'll try to be really friendly (well except old crotchety Monaghan