Sounds like you have extended your desktop rather than mirroring it (to prove ... whizz your mouse pointer to the far left or right and see if it appears on the TV.
to stop it ... go to display settings (you don't say which OS so can't be specific)
and take the tick out of the extend desktop option.
then on your laptop (you don't ay which model - so no specifics) look at the "f" keys (mine is f5) for a greyed pikkie of a monitor.
Press and the fn key ... + whichever f key and the display will cycle from lappy - lappy + monitor - monitor (tv).