Why is it that

when I look down at my penis it looks pretty small, but when I take a picture of it directly afterwards on my cell phone it looks a lot bigger? I will literally compare the picture with real life. Did I just develop a complex or something?

Your cell phone must be equipped with an OEC, or Organ Enhancement Chip. Just don't take a picture of your girlfriends rear end with it, or she'll diet for months.

Also, it made me realize I have pretty humongous balls complimenting my average sized penis. Kinda strange. I'm only 19 right now so hopefully my penis can catch up a bit before I fully stop growing

Generally you get a foreshortened perspective on your member, due to it's location relative the eyes. Lift it up towards your face and bend down and you'll notice it looks a lot bigger.

Cell phone digital cameras are literally the cheapest optics you can get that does the job. Because of this, they often distort things.