Hi, My Child Is 18 Months And He Was Prescribed

Hi, my child is 18 months and he was prescribed amoxicillin for an ear infection. I gave him 6ml at 9am. My sister was watching him and i told her the directions for giving him the medicine every 12 hours, but she forgot and thought i told her just to give him the medicine at anytime and ended up giving him another 6ml dose at 4pm. Will he be okay????? Do i need to take him to the ER to be checked??????