is there a way to limit the entities in the confirm rule? i.e I only want one entity in the result

What if you went into the Calculation Definitions Tab of the Workflow Profile, and used the "Confirmed" switch which (per ref guide) " determines whether or not the Entities defined by a Calculation Definition should be subjected to the Confirmation workflow step. It also gives the application designer control over which Entities are subject to the Confirmation Rule validation process."