Here's the backstory

I recently went a vacation to a large Caribbean resort where there were plenty of people my age (20). The first night the resort was hosting a 'Meet and Greet' type event, and so my friend and I decided to attend it, if only for the purpose of finding out who we'd be seeing all week long.

So I walked into the room where the meet and greet was being held and deduced that this would be an excellent time to work on a few techniques. We arrived to the event about 20 minutes late so everyone was already seated in circle of sorts. Upon entering the room I noticed that a single girl was was focus of attention; lets call her Amy. I decided that I would act confident and try to take some of the spotlight. I instantly introduced myself to everyone, and made sure to make conversation with the Amy in which I was the leading conversationalist.

For the rest of the evening I felt firmly in control of the conversation around me, and in general you could say I was the new focus of attention. I was sarcastic, witty, confident, always made eye contact, etc, etc. However, it wasn't really until the second night when a few of us were drinking that I noticed that Amy was flirting (both verbally and physically). Obviously, It was relatively easy to move forward at this point and by the end of the night we had made out, but didn't get much farther than that.

The problem with all this is that I'm naturally not the person who I pretended to be on those first few nights. I'm not shy, and can be the center of attention when I want to be, but I much prefer private conversations and intimate encounters. I'm not as overtly confident as a portrayed on that first night, and I'd be careful about calling myself witty in any sense of the word. I wouldn't say that I was unauthentic, but I certainly exaggerated certain features of my personality which made me seem more "alpha".

I hung out with Amy on the 3rd night, but by this point I was tired of playing that exaggerated version of myself, and perhaps a little hungover. So I consciously reverted into my regular self. It's not like I was fixated on sleeping with this girl, so I honestly didn't mind if I lost her or not. It would have been nice to keep going with her but unfortunately by the 4th night she wasn't interested anymore and with some other guy.

Admittedly the other guy was extremely attractive, sort of withdrawn, and good at karaoke. He seems to have his game down to an art, so I didn't mind losing out to him. Actually, he turned out to be a pretty cool guy and bought me some shots later in the week. No hard feeling what so ever, especially over some random girl.

Now, my question is how can I avoid losing a girl when I shed that original persona and revert my regular, more comfortable, self. It seems to be a common theme that I can pick a girl up and keep her interested in this fake personality for a while, but once I get tired of keeping up said front the girl tends to lose interest.

I'm not saying that I cannot pick girls up when I'm being myself, but I'm definitely less effective without the "first impression" persona. Does anyone have any experience with this phenomenon?

I can go into detail on what I do to achieve this "first impression" persona if you guys ask. I feel like I've posted enough in this OP though.