You don't really need to make the sphere larger than your world. You can just change it's Z order so it gets rendered before anything else, then it will appear behind everything. Move it with the camera so you'll always be inside.
Graphics3d 800,600 world = LoadMesh("level.b3d") ;load your world sky = LoadTexture("Sky.png") ;load the sky texture skybox = CreateSphere() ;create your sphere for the sky FlipMesh skybox ;flip the surfaces to the inside EntityOrder skybox,1 ;change the entity Z order so it will be drawn first. EntityTexture skybox,sky camera = CreateCamera() While Not KeyDown(1) UpdateCameraPosition() ;Some function used to read input and update the camera view accordingly PositionEntity skybox, EntityX(camera),EntityY(camera),EntityZ(camera) ;move the skybox to the camera's position RenderWorld Flip Wend