Looks like you're trying to install it manually by typing all the lines of the script one by one. It cannot works this way. Here, it complains about $WEBROOT/panels/op_server.cfg.fws not found but:
in the script, it's $WEBROOT/panel/op_server.cfg.fws (without the 's')
and $WEBROOT is a variable defined in the script, and it's value is /opt/asterisk. Outside of the script, this variable is not declared, so it'll have an empty string as value.
You should really let the script do it's job.