Don't bash yourself... Even if you have had done the biggest major mistake you could possible do with a girl, the most AFC thing ever, learn something from it, but why feel bad about it? You still can like yourself. You can choose to keep liking yourself despite the mistake, so it doesn't matter. The only real bad thing that can happen here... Is that she doesn't like you. You still like yourself, so what the heck. It's not like it's some sort of stupidity to not have "game", it's fairly common as we can observe... So lets not bash ourselves too hard. Just keep improving. I tought it was suspicious that you said: "I feel like a retard for saying that", anyone with me on this one?
You say "I should have hit her with some negs and a challange", why? So she can like you and you validate your ego? Or cuz you want to get laid? Maybe both... But there are many more girls out there. My advice is to stop thinking what to say to gain her approval. Don't play a game like: "Oh now it's time to neg", "I wanna go there but I gotta remain a challange". Isn't that stressing? Why not forget about the "DJ rules" completley, not stress about girls at all "She likes me, she doesn't" or "I got to say this, say that, etc". If you have self esteem you're going to naturally do attractive things anyway, so isn't it a better idea to not worry if she likes you, and try to get her to like you, instead why not just work on your self esteem and build natural game? Id forget about these tactics like "I got to remain a challange" and etc, just work on your happiness and your life, if one girl dumps you who cares?