I am connecting my MACbook Professional with my HDMI twine to my TV.
Once I join, the primary display on the pc shrinks. Once I take away my HDML twine, the display it goes again to the identical dimension.

How can I stop it from shrinking and all stay the identical dimension?

Ken Robol is a brand new contributor to this web site. Take care in asking for clarification, commenting, and answering.
Take a look at our Code of Conduct.