Why does Gene lie about living by the rules?

In Chapter 5 Gene decides he'd better be getting back to the station, since he's a day late, and lies to Finny, telling him that he won't be playing by the rules any time soon. Outside of Finny's influence Gene generally followed the rules. Within Finny's company Gene wanted Finny to believe that he was the same person, who followed excitement and rebellion, when they were together.