Matrix scale issue - c++

Question

I am trying to apply scale, but nothing happens. Looks like scale() matrix is incorrect? I tried simply to copy formula, but id doesn't help.
glm::scale(mat4,vec3);
Any help would appreciate.
void specialKey(int key, int x, int y) {
switch (key) {
case 100: //left
if (transop == view) Transform::left(amount, eye, up);
else if (transop == scale)
{
sx -= amount * 0.01;
std::cout << "left scale";
}
break;
case 101: //up
if (transop == view) Transform::up(amount, eye, up);
else if (transop == scale) sy += amount * 0.01;
break;
case 102: //right
if (transop == view) Transform::left(-amount, eye, up);
else if (transop == scale) sx += amount * 0.01;
break;
case 103: //down
if (transop == view) Transform::up(-amount, eye, up);
else if (transop == scale) sy -= amount * 0.01;
break;
}
glutPostRedisplay();
}
mat4 Transform::scale(const float &sx, const float &sy, const float &sz)
{
glm::mat4 mat = glm::mat4(
glm::vec4(sx, 0.0f, 0.0f, 0.0f),
glm::vec4(0.0f, sy, 0.0f, 0.0f),
glm::vec4(0.0f, 0.0f, sz, 0.0f),
glm::vec4(0.0f, 0.0f, 0.0f, 1.0f)
);
glm::vec3 vec_scale = vec3(2.0f);
mat4 ret = glm::scale(mat, vec_scale);
return ret;
}