What kind of errors are you getting ? It would be helpful when troubleshooting.
Also, please check if you have opened port 8000 in the GCE firewall. You can test from your local machine, like this : $ telnet <instance_IP> 8000
If you do not have the port open, run this to create a rule : $ gcloud compute firewall-rules create ajenti --allow tcp:8000
Hope this helps !