He kisses her again immediately, just because of the vague hint to stop. Not only that, he just really wants to keep kissing her, but spite seems like a good reason, even if he's the one who is more interested in the actual date.

Cassian just really wants to be close to her right now, it seems very important that it's right now, and apparently part of that includes kissing. Jyn never seems to mind. "Keep what up?"

Maybe he's gonna play dumb though. Because maybe he's gonna kiss her yet again, only this time it's on the jaw while his hand moves to the small of her back.