I fell 3 days ago in front of a prominent store due to eneven sidewalk can I sue them?

You can sue whoever has the legal duty to ensure that the sidewalk is properly maintained. You need to have photos of the sidewalk with a ruler placed so that the amount of unevenness can be determined. Once you have this information, then you should meet with a personnal injury attorney to discuss your options. You did not mention whether you were injured.  If you were not injured to the extent that you required medical treatment, your fall may turn out to be a no-harm-no-foul situation.