Dang OP, your analogies are making me hungry...
OT: I am a little confused about this bet... but from what I gathered, you win by default. Basically, don't do shit. Then, you win the bet (or lose it?) and your truck is payed for.
Be mindful, however; the female mind is a fickle thing, and she is likely testing you. As in, she is rewarding you for failure, and I am sure she has a reason for that. Here are my theories:
1. She believes in your abilities to pick up girls, ie she has faith in your self-confidence. Further, she trusts you enough to think that you will still respect her as a woman while you are discovering yourself through other women. If this is the case, then you should definatly try to let her win, as she will likely lose respect for you otherwise. Even so, remember that no girl, whatever the circumstances, wants to have a boyfriend who fools around with other girls. In short, show her you have what it takes to be a man, and then prove that no woman matters to you except for her.
2. She is testing your obedience. While she says "I want you to find another girl" what she really means is "You better not though." I have seen this particular maneuver in action (so to speak) and the best way to handle it is to remain completely faithful. Prey that this is not her goal, as it would mean that she is a conniving, manipulative, overly sensitive *****. I doubt very much that this is her motivation, but you know her better then I do.
3. She's cheating on you, and using this "bet" as an excuse to leave you for another guy, yet justify it with "but we agreed to be open, and this was bound to happen". keep an eye open for "the signs" but don't assume anything, and especially don't confront her about it. Not trying to scare you, though; out of my three ideas, this seems the least likely.
4. none of the above. I am certainly no expert on female motivation, and my experience in dating them is hugely stunted by my homosexuality. In the end, you know her better then any one of us. Your best option is to go with your gut instinct, and to have faith in yourself (after all, that's what all this is really about, right?). If you can improve your own self-confidence and self-image, then whatever happens, you win.