Unable to sync all AWS instance server onto Ansible Tower

I have around 30 Server Instances in AWS all having only the Private IP.
In the ansible tower, I have used AWS access key and secret key and thus configured the credentials in the tower.
When I start creating a new inventory, i fill all the necessary params in the inventory sources and then I sync the inventory. After syncing, I am able to see 2 or 3 instance in the host tab.
I cannot see other hosts.
Please help me resolving this issue.

Are the ec2 instances enabled? You can try running the dynamic inventory script manually to see how the results differ https://github.com/ansible/awx/blob/2.0.1/awx/plugins/inventory/ec2.py