There is not a contingency for this particular situation in SC, you may need to speak with your agent or attorney. Sorry, I wish I had good news for you. Vicky pretty much summed it up regarding Megan's Law.

In VA there is a disclosure you must sign with a real estate contract that tells you that you should do your own due diligence with respect to Meagans Law (thats the sex offender registration requirement).... but it is not a contingency. You are assumed to have had the opportunity to check this PRIOR to submitting an offer. There may be another way out.

As a mom of 4, I get it, but keep in mind after you buy a house, a sex offender can move in next door. Will you sell then? Also, it is hard to tell a really scary bad guy from a not-so-bad guy on these lists. For example, if my otherwise law abiding 20 year old was to date a 17 year old, he could be prosecuted for a sex crime that would require him to register. That's not the kind of guy I am afraid to live next to; but it is hard to tell that from a child pornographer or molester which would scare the dickens out of me - and YES, in that case, I would probably sell MY house, too.