2d Texture Rotation Problem

Hello. I have created this shader to rotate the texture, but the axis of rotation is not that I want (see the picture). How can I fix it?

 Shader "Decal Rotation" {
 Properties {
 _Color ("Main Color", Color) = (1,1,1,1)
 _SpecColor ("Spec Color", Color) = (1,1,1,1)
 _Emission ("Emissive Color", Color) = (0,0,0,0)
 _Shininess ("Shininess", Range (0.01, 1)) = 0.7
 _MainTex ("Base (RGB)", 2D) = "white" {}
 _DecalTex ("Decal (RGBA)", 2D) = "black" {}
 }
 
 SubShader {
 Tags { "RenderType"="Opaque" }
 LOD 150
 Material {
 Diffuse [_Color]
 Ambient [_Color]
 Shininess [_Shininess]
 Specular [_SpecColor]
 Emission [_Emission]
 }
 Pass {
 Lighting On
 SeparateSpecular On
 SetTexture [_MainTex] {matrix [_Rotation] combine texture * primary double, texture}
 SetTexture [_DecalTex] {combine texture lerp (texture) previous}
 
 }
 }
 
 Fallback "VertexLit", 1
 
 }

The script attached is:

 public bool RotateMainTexture = true;
 
 void Update()
 {
     if(RotateMainTexture)
     {
         rot = Quaternion.Euler (0, 0, Time.time * rotateSpeed);
         m = Matrix4x4.TRS (new Vector2(0,0), rot,new Vector3(1,1,1));
         renderer.material.SetMatrix ("_Rotation", m);    
     }
 }