You made almost all the right moves.
Good idea to tell her that you have a girlfriend. That's what I would have done.
The only obvious screw up was the massage part.
Your next move will depend largely on what sort of girl she is. You may get laid on the next date, or you may screw up for going to fast.
One obvious thing you must do is to avoid becoming too familiar. Consciously avoid becoming assexual or creating an assexual bond with her. Do at least one naughty thing. Even if your nest meeting is to sit down for a casual coffee at the cafeteria. (Get stooged friend to wolf whistle at the two of you and wave back casually as if it were expected, for example - maybe too old a trick. I once tied a plastic band on a girl's ankle as an anklet after explaining that the same band was used as handcuffs in certain places. Be creative. But not too lewd. You get the idea.)