Vertex shader help with scaling

[Wayfarer]

I'm doing a lot of guesswork here as I'm new to shaders.

In the vertex tab, I've noticed if I multiply "in_Position.x * 0.98" I can offset the shader to the left, which is interesting, but not what I need!

void main()
{
    gl_Position = gm_Matrices[MATRIX_WORLD_VIEW_PROJECTION] * (
        vec4(in_Position.x * 0.98, in_Position.y, in_Position.z, 1.0)
    );
    v_vColour = in_Colour;
    v_vTexcoord = in_TextureCoord;
}

How would I go about scaling something, say 4x?

The shader is applied to individual sprites like so:

shader_set(...);
  draw_sprite(...)
shader_reset();

Edit:
Ah, I now see that "gl_Position" is setting the position. Hmm. Is scaling possible?

Edit2:
Do I get the sprite coordinates with sprite_get_uvs() or something?