Oracle 11.2.0.3 Service Name Mismatch issue
SERVICE_NAME is made up of the values db_unique_name and db_domain parameters. Here is the reference to Oracle Documentation about SERVICE_NAME. Even if you set lab3 as service name oracle automatically adds value of db_domain on it. Your service_name is 'lab3' and db_domain is 'domain.com' so you end up with the orgianl service name.
Instead you can create tns service name to point that service. Example is given below

lab3 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = domain.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = lab3.domain.com)
    )
  )


Then you can use this tnsname(lab3).