It is not, in Cal's experience, difficult to get around his mother's decrees. He just has to disobey in a manner that lets her pretend not to notice.

Which, when he's out of the house, isn't hard at all. It's Peter who follows the minutiae of Cal's movements when he's being followed, and the fact that he never even mentioned to Mother that he caught Sherlock sneaking in speaks volumes all by itself. Cal is pretty confident that a visit to the Stark residence will go similarly unmentioned.

(He's not wrong. Peter's been out this way to check out the Stark property, and one look was enough to tell him that Cal is safer here than he would be anywhere else in Sunnydale.)

Which all boils down to Cal driving up the driveway, grabbing his backpack, and heading to the front entrance without any hesitation.