As I understand it, the calculations you have worked through give you a % w/w solution rather than a % w/v solution. Weight/volume percent solutions are odd in that they actually have units, usually g/mL. All you need for a 4% w/v solution is 0.04 g/mL. This is read "0.04 grams of solute per milliliter of solution" (not "per milliliter of solvent"). The mass of the solvent doesn't come into consideration, only the total volume of the solution.