30 day stay visa, tickets for 63 day stay.

I have only been given a 30 day stay visa but need to be in China for 63 days (and purchased a return ticket some time back for these dates). The lady at the visa office said to ask for an extension once in China and that it shouldn't be a problem be she couldn't guarantee this of course. I am looking after 3 children each morning whilst their mothers study at Shaanxi Normal University. My question is, if I turn up at the airport with tickets which show a return date 30 odd days after my allowed stay expires, will they even let me into China to begin with?