Can you please check your system date (current date on your mobile). You may not modify the date of exisiting sticky note , but delete the old sticky note with wrong date and create a new one, once the system date is correct.
I have the same problem. Have read both answers but in my case the date is wrong by a month and a half although it does change by one day each day. Is this the same for you? I'll be following this to see if you get a good result.