With show only related records, GTRR will bring up the same records as listed in the portal, but with the clicked portal row record being the current record. You can add steps afterwards to isolate this one record if you wish, or keep the detail layout in form view (just hides the other related records from immediate view), or you can perform a find for the record on the detail layout instead of using GTRR.
Show All Records
Show Only Omitted
will isolate the current record in a found set of one record in single user set ups. In multi-user setups, there's a slim chance that a record created at the same instance as this script may show up included with the record you want to isolate.
Using Find instead of GTRR:
Set Variable [$PrimaryKey ; PortalTable::PrimaryKeyField]
Go To Layout [detail layout (PortalTable)]
Enter Find Mode
Set Field [PortalTable::PrimaryKeyField ; $PrimaryKey]
Thanks for the help that did the job