I have a growth underneath my skin under my scrotum is it just a pimple to pop or is it cancer?

Not likely to. Be cancer. Don't pop it, but you can soak in warm water in a tub and use soap. The adjacency to your rectum, not the cleanest part of your body, makes "popping" a bad idea. See a doctor to make the call and do the dirty deed if needed.
Probably infection. Abscess are more common in this area than cancers. Apply warm compresses to the area and if does resolve or worsens see your primary care physician.