So, the long & the short of it is that you prepared all of your time sheets at one go and had the dude sign them - and you didn't show him proof that those were the days you were there and he didn't bother to check. And in all likelihood, the powers that be chose that particular timeframe to audit attendence.
I suspect you've got a serious problem. You may want to check the school's policy on appealing these sorts of things, and possibly talk to an attorney. But you may be well and truly screwed unless you can provide definitive proof that you were there the days you claim to have been there.