This is probably the wrong site for your question - the majority of us are Brits, and we find the notion of tipping embarrassing at almost all times.
As you may be aware, tipping is not culturally essential in the way it is in North America, but as I understand it from my visits there, fifteen to twenty per cent is considered the norm.
On that basis, if your piercings cost $200.00, you were on target. If it was much less than that, then you were perhaps generous, but without knowing the final bill, it's difficult to assess.