Before applying the template, you need to add some entries in the SCC:
oc adm policy add-scc-to-user anyuid -z default -n <namespace>
oc adm policy add-scc-to-user anyuid -z <application-name>-user -n <namespace>
oc adm policy add-scc-to-user privileged -z <application-name>-runner-user -n <namespace>
The application-name will be passed to the template, the default value is gitlab-ce.