port mapping didn't happen for a container deployed on AWS ECS(uses EC2)
Since you are using Network Mode: awsvpc the container will have its own IP address and will not use the IP of the EC2 instance. You can find the container's IP in the running task details.
Alternatively you can use Network Mode: host where the task will share the IP of the EC2 instance and will be accessible on the instance IP port 3000.
Hope that helps :)