Honestly I really don't think there's anything you can do or say to smooth this out, because I highly doubt your parents will stop believing what they do.

I say you should just grow a spine and not give a rat's ass what they think because what's done is done. What's that saying again? You can't teach an old dog new tricks.

I mean seriously, what are you going to do to try to appease them? Give up sex until you're married? Mon, you know that won't happen.

Just apologize for being a huge disappointment to them and move on.