You can't make the scent of copulins smell "better" per se, the compound was specifically created to emulate the scent of vaginal secretions and therefore it has to smell as it does to do what it does. What you can do is find the balance between the amount you use and the fragrance you use to cover it in order to get the result you want.
Guys may possibly think copulins smell bad, but they have to be able to smell the compound in order for it to have the desired effect, at least a hint of it.