Assuming that your polygraph was not conducted by a federal law enforcement agency, I would not expect your polygraph results to come up in the course of a background investigation.

As to why the polygraph operator would not show you the results, you have to realize that polygraphy is a fraud. It has no scientific basis, and the offer of a polygraph "test" to criminal suspects is a ruse to get them into an interrogation room without a lawyer present. The suspect's "failing" the "test" can be foreordained as part of the interrogation plan.