So, Apparently I am a slut for expressing myself at the age of 13?

As long as your parents are ok with it and you're sure you want it then you really shouldn't care what others say. By the way the people who called you a slut should really keep their mouths shut because they obviously don't know the meaning of that word. Just ignore them hun, as long as you're happy with your piercing then it's all good ^_^