Merchandiser

As a part time employee merchandising for Pepsi, am I mandated to work 40 hours and overtime? Can someone let me know? I wouldn’t mind the hours as a full time employee. When I applied, I was hoping for full time only for them to say I was going to be part time. Now it’s been a month and a half and I’m working more than full time hours with no full time employee benefits or coverage. So .. no thanks if I don’t have to. Someone enlighten me.