You want to be sure to have the cloth flat and not raised as the sanding will cut through it when trying to smooth the surface. From where I live it looks like there may be some wrinkles in the cloth. It does matter as much on the outside as it does on the inside. I saturate the surface with epoxy and lay the cloth on the wet surface pressing it smooth and then giving it a coat of epoxy to cover it completely and allow it to dry and sand. Then repeat.
You may have better luck by laying the sink on one side and doing one side at a time allowing it to dry before moving on to another side. That way the epoxy will not run down the side but lever out more.
