The scandal wasn't that they broke into the hotel. It's because they broke into the National Democratic Headquarters office, which was located inside the Watergate hotel. The five burglars broke in to place bugs (microphones and phone taps) in the office so that Nixon could spy on his opponents.
Nixon was never actually in the hotel. In fact, of all the people implicated in the burglary, Nixon was one of the last people revealed to have been involved.
If you want more info on the burglary, I recommend the movie "All The President's Men," starring Robert Redford and Dustin Hoffman.
Don't watch the movie "Nixon," because lots of that movie was fiction, and not at all reliable for historic reference.