Lightmapping on a custom shader

Hey guise first time question asker and need help plox.

Im using this shader to make my object double sided but when I apply lightmap to it, it goes invisible and i can just see the mesh. Any ideas? Im also getting a message in my lightmapping window saying "Objects size in light map has reached max atlas size".

Cheers in advance.

Shader im using:

  Shader "DoubleSided_IF/Diffuse" {
         Properties {
             _AmbientColor ("Ambient Color", Color) = (1, 1, 1, 1)
             _DiffuseColor ("Diffuse Color", Color) = (0, 0, 0, 0)
             _Emission ("Emmisive Color", Color) = (0,0,0,0)
             _SideOne ("Side 1", 2D) = "white" {}
             _SideTwo ("Side 2", 2D) = "white" {}
         }
      
         SubShader {
         Pass {
             Material {
                 Diffuse [_DiffuseColor]              
                 Ambient [_AmbientColor]
             }
             Cull Off
             Lighting On
  
             SetTexture [_SideOne] {
                 Combine Primary * Texture
             }
         }
  
         Pass { 
             Material {
                 Diffuse [_DiffuseColor]              
                 Ambient [_AmbientColor]
             }
             Cull Off
             Lighting On
  
             SetTexture [_SideTwo] {
                 Combine Primary * Texture
             }
         }
     }
 }