I met this HB9 a couple weeks ago, I didn't really talked too her much after my initial approach. Two weeks later, I find out that she is working at the grocery store where I always do my groceries. So I decided to chat her up at the register. I got her number. She texts me saying she is hosting a party at her place. No too big of a party around 6 other people just hanging out. After the party we two are left watching a movie. we had sex that night.

I have no rapport with this girl.
Only build some attraction.

After a couple of days she invites me to her place again, with the same crowd as last time. This time however I had almost no interaction with her. Instead she flirts with some other dude. I ignored the flirting part.

After everyone left, she was yawning, saying she was tired. So I told her that I was going home. She gave me a kiss on the mouth and said bye. The vibe we had on the first night is completely gone.

What did I do Wrong?

She re-invited you... And kissed you on the mouth when you left. You were expecting another fuck and didnt get it so you're dissecting the shit out of this.

Maybe she wanted you to escalate and you didn't. Whether she was flirting with the other guy or whether you just saw it that way cause you wanted to close is up in the air. I wasn't there, you were.

What'd you do wrong? Not escalate from the sounds of it - based on the details you provided.

So you've already fucked her once, you are there alone with her again and you kiss her and leave? Lol... Yeah tough one here.

As you are leaving, grab her butt, kiss her neck, you know the rest.

She's tired? So what? Just do it son! If she shuts you down THEN you may have fucked up with your behaviour/body language/whatever. You didn't even try!