That's cool that you got great reactions and sparked peoples interest, but you broke the cardinal rule of magic. Don't do the same trick twice for the same audience. The first time they are entertained, but the second time, all they care about is figuring out how the trick is done. Regardless of whether you nailed the tricks the second time or not, just don't do them twice. If you need good excuses for not doing the trick again, look at the outs and one-liners forum. The best way to avoid this is always bring more props then you think you'll need when you perform. Just always be prepared. On the Spot really comes in handy doesn't it?
If you want to read a good example of an impromptu killer performance, check out the post I made earlier.
http://www.penguinmagic.com/discuss/vie ... p?t=119919