You will most likely be fine. Even though it is not recommended to take more than 1000mg at at time and 3000 mg in 24 hours, usually it takes 8000+ mg to do damage. This is not to say that it cannot happen at the dose you took so if you start getting severe n/v, abdominal pain, jaundice etc seek medical help. Symptoms can take up to 72 hours to manifest but I think you should be ok. But it never hurts to get checked if you are worried.
Were there other ingredients besides DXM and APAP?