I took 2x400 mg of Ibuprofen all at once, I'm 13 years old. I also took 2x400 mg more, an hour earlier. Should I be concerned or worried?

You'll be fine.

Be aware that ibuprofin is tough on the kidneys.
What I do when in pain is alternate ibuprofin with tylenol. There's a third kind of OTC pain reliever in Alleve, naproxen. Each may work differently on different kinds and areas of pain, and differently for each person. Remember the 3 generic names
Ibuprofin
Acetaminophen
Naproxen