Got a job offer but messed up on employment date, please help!?

Most companies do check your employment. Not to worry, if they are interested, they will ask you...be honest and let them know it was a mistake. It happens and it is not a big deal...it happened to me. When they ran my background check, I realized it and told them that I goofed on the date. Since it was a honest mistake and not a lie about your employment, most companies will understand.