Damn, I dunno if I'd be up for a date on the same day my potential son/daughter was turned into Purina dog chow. At first glance, it does seem a bit cold-blooded of you to paint the town red on such an occasion, but that's easy for me to say cuz I never been in this situation.
Maybe you legitimately needed to escape and decompress from such a bad experience. Perhaps you were just fed up with this chick dragging you down and making your life miserable ... or maybe your date was THAT fine!
Either way, none of us can really judge. You had your reasons and ultimately your conscience should be clear because you did offer to do the right thing. Like the others have said, this was ultimately her choice and she has to live with it now.