Please get your dog to the vet. Better to be safe than sorry.
Welcome.....You don't state what size dog this is....That information is crucial....If this is a small dog and 3ml is a human dose, then yes, it could be harmful.....A large dog would be less likely to suffer as serious side effects.......
The same overdose symptoms can happen to a dog as with a human.......You need to look at your package warning label and read them or google side effects of this medication......
If you see anything unusual with your dog's behaviour, you need to seek medical attention ASAP.....Let us know how he/she is doing.....Karla