I hope you mean you cut your scrotum and not your testicle, because if your did cut your testicle that’s a pretty deep nick.:) Getting a cut or nick on your scrotum or penis is no different than getting one anywhere on your body. Been there; done that. If your keep it clean and dry it will heal just fine. If your need a little psychological lift you can use a little of any of the things I call “voodoo juice” (bacitracin or betadine solution) - maybe they work; maybe they don’t. They can’t hurt.
I know, when you cut your guy or his sac of friends, it feels pretty concerning. But I’m more concerned about nicking my face shaving - it’s more noticeable (hopefully, or you’ll get arrested) and people might think I attempted suicide (or at minimum, that I don’t know what I’m doing when I shave)..