3D Disable mirror effect.

I have a counter strike 3d weapon

and a 2d file with the texture for the 3d weapon.

When I paint on the 2d texture file on the left side of the weapon

and try to place the 2d texture file on the 3d weapon then I get a mirror effect.

The paint I made on the left side will show on left and right side.

Any chance I can disable the mirror effect and how.?