What are the consequences if caught falsifying timesheets?

For about 5 months now i was "fired" from a temp job I was working for a couple months but it was a weird ending. The guy at the job said I needed to call the temp place and see if I was going to be brought back. So I called three times asking if I could go back to my recruiter and the response was I still havent talked to the head guy, so i'll see. Well times were tough and I just happened to put in a full online time sheet like we usually do. And it was approved for pay. So I've continued to do it because my job situation remained rocky and I had to maintain my family. The company continues to email me saying that my timesheets is over due when it reaches the over due point. Blinded by maintaining my family, I have recently more been thinking about the legal issues that could arise because of this situation. Could you please tell me what could legally happen, and the consequences. Thank You.