Seduction Worked but on the 1st Date, She Lost Interest

Heres a story of a hot girl I was seeing in Salsa classes, I took alot of my sweet time before I hit the target.. I used to 'stealth seduce' her during the dance class. It worked, she liked me and started teasing me whenever I danced with her, we discovered that were from the same background and he interest was at its peak. (I personally cannot do quick or direct openers and need an occasion to make a move)

One day I stretched the convo and she wanted to talk to me further about all the stuff but she had to go to the advanced classes; she also said, It would be great if you come to that Salsa Dance Party that is 3 days away. I told her let me see and told her that you could add me on your blackberry contact list which she did.. Since we had more stuff to discuss..

On the afternoon of the day of the party, I had a brief text chat on the phone with her and to see if she's going on that night.. She said yes.
So I went there that night and she was happy to see me and all. You could see the interest and some nervousness on her face.

The beginning all was going well, I was not the best dancer but I took the dive anyways since its a salsa party.. Slowly I started feeling like shes getting cold and distant.. And slowly she started going and dancing with other people; those who are better dancers than I am..
Moments later I felt the coldness and I started to lose faith in the situation... I felt she's only standing next to me for the sake of not being rude so I said Ill go out and light a cigarette..
Suddenly I was outside and I saw through the window a guy approaching her and starts a convo. I see him and her take out the phones and exchange numbers..
I walked back in frustrated from the situation as I assumed I was the guy she was interested in from the 1st place.. The other guy stayed standing in near proximity and I didnt know what to do about him.. I took her for another dance to drive him away but as soon as the music is over we go stand in our corner and she automatically initiates the conversation with him as if im not there..
At that time I gave up and told her: "Listen, I gotta go as I have a big day tomorrow and I live in the next town so there's a long drive to do.."

I believe I have done a handful of mistake there. I even tried to on a couple of other girls but one thing that made it hard was the huge competition from other guys there and the fact I was also frustrated of the situation..

As a side note: Some of the stuff that Shatters me when approaching women is:
1. The fact I dont do it often and barely had dates in my life
2. Thinking too much of the techniques and game