It certainly does look like a Tahitian, although it is light in color. Darker pearls, especially those with peacock coloration, tend to be quite a bit more valuable.
As for the price... again, you did not get ripped off, although it is high retail. 330USD is what you would expect to pay, more or less, in a retail jewelry store.
However, for the same price online you can get something like this:
http://www.purepearls.com/detail.aspx?ID=370
Or most of the pieces here:
http://www.pearlparadise.com/Tahitia...ants-Rings.htm
Or this piece:
http://www.pearlsofjoy.com/index.asp...ROD&ProdID=166
And several pieces here:
http://www.thepearloutlet.com/tahiti..._pendant_1.htm
If an online seller were to make the identical piece for you it would likely be well under $100.
The comments about the nacre and value, that is just pressure selling, and unfortunately it was not really true.
But the piece is nice enough, and the surface looks clean from the photo. It is a genuine Tahitian pearl, and it was sold as such. You did fine.