Don't feel too bad as even more experienced collectors make mistakes, and I've made many worse than you just made. However, I'm not sure how much of a mistake it actualy is. Some collectors want pristine pieces; others (me) are less concerned. Hand blown glass inevitably gives rise to imperfections, some of which I'm happy to accept, such as broken bubbles on the inside of the piece. I've got an Ohstrom Expo piece that has a little bruise on it, which I show quite happily. As I type I look up and see a a Palmquist Kraka piece with a stress fracture (bought for $9.75, I'll admit) that still gives me pleasure, and I've got a studio glass piece that the maker told me was a second, as he didn't quite get the effect he wanted. It looks great to me and I got it for 1/2 price. The key thing to me is whether I like it in its current state. Of course, it would concern me if the seller had misrepresented it to the extent the price was out of line, but I would still think about whether I liked the piece.
Do send a picture in and/or try to locate another picture some where on the net or in a book so you can compare your piece.