The majority of TVs have a default setting called overscan which causes part of the screen to be cut off when you are duplicating your display to the TV screen. This is due to the variation in screen sizes that are transmitted between national / international TV broadcasters.
The good thing is that this can be typically resolved in the majority of newer TV models easily within the TV menu settings.
However, as the manufacturers don't want to be seen copying each other they ALL have different names for the same thing! This makes it a little more difficult to give a general overview, however, you can typically find it under Picture / Source / Format under your display settings - once you've got this, simply switch it OFF. Another way to capture the correct screen is the match your computer display settings to the TV display settings.
To find the specific settings on your TV, you'll need to head to the support page of your TV manufacturer directly.
Just insert your TV model into search function & it should bring up the manual for you.
If you are interested in learning more about overscan, here is an article from Engadget that gives a good overview of the technicalities of the problem and how to solve it.
Examples of adjustments
On this TV the overscan can be removed together with adjusting contrast and sharpen for sources like Airtame and computers in the Advanced settings menu.