Need advice about my maternity leave at work

Ok so I didnt know where to ask, so maybe you guys can help. I started a job in Feb, and started my unpaid 6 week leave July 20th & had my baby the 24th. I was sent paperwork in the mail a few weeks ago that I was supposed to take to my doctor saying when I could go back to work etc but I never sent it in ( part laziness , part no one to watch baby because babies are not allowed in your appointment) . Im supposed to start work next week but Im scared to go tell them I never got my doctors note. Do you think I can go get a doctors note now anyway saying im able to work?? Im in california , i work at a grocery chain