Theory:

We all know that there can be two or more lines of symmetry.
 
Let us look at a few examples with exactly two lines of symmetry.
 
Picture1.png
 
In the above example, the same shape can be cut into two identical halves in two different ways.
 
So the same shape with both the lines of symmetry will look like this.
Picture2.png
Let us also look at a few more examples with exactly two lines of symmetry.
 
Shape
Lines of symmetry
Final figure
Picture4.png
Picture3.png
Picture5.png
Picture8.png
Picture6.png
Picture7.png
Picture10.png
Picture9.png
Picture11.png
 
The shapes mentioned above will only have precisely two lines of symmetry. No other line can cut these shapes into identical halves.