Recently a same thing happened to me, but with 20 clicks! (Not that 20 clicks is odd as it is, but I was having 2-3 clicks a day in that ad unit) I was totally freaked about this so I decided to talk to the big guy :)

I sent an email to Google explaining what happened, I offered to show the logs and told them to please discount the earnings as I thougth those were invalid clicks, maybe from a spam bot or a malicious person.

I got a respond telling me that they had already discounted the clicks, and that everything would be okay as long as I didn't do anything against the rules.

So, I think that your best bet is to report to Google and check that everything is ok.

Cheers!