I would still flag that for a student, mostly because it makes it unclear when things are happening. The first part is okay, and the "I hope the drinks are cheap, but Paul said he would cover for the drinks" works fine, IF you mean that Paul promised this before you got there. If he promised you that while you're standing there (as in the dialogue) then the same tense should be used. So this would be the timeline:
Paul promises to pay for drinks THEN you go to the nightclub together AND NOW you're standing outside the nightclub.
Asheley swung her purse is still wrong, because she is doing this while standing outside the nightclub, which is your story's present time.
Basically, in any writing, be it a blog, facebook or a story, you need to make up your mind of when NOW is (the story now), and keep tenses accordingly. So if NOW is the time of writing, then everything should be in past tense - You were standing, Paul promised and Ashley swung her purse...and NOW you are writing. If NOW is the time of the story (when everyone is standing outside the nightclub) then everything that happens at that time needs to be in present tense. You are standing, Paul promises, Ashley swings her bag.
Say the scenario is we've already been standing outside the night club for a while, and then I am posting about it say on Facebook as:
We're just standing outside the Blue Velvet right now.
But before I posted that on Facebook. Paul already said that he would pay for the drinks, and Ashley already swung her purse.
Say, I'm trying to tell say my Facebook friends that we're just standing outside the Blue Velvet right now, but I am also trying to say that Paul said he would cover for the drinks and Ashley is so excited that she was swinging her purse. What Paul and Ashley did happened in the past, but I am telling my Facebook friends that we're just outside the Blue Velvet right now even though we've been standing outside the Blue Velvet for a while.
What I am trying to do is say that we're here right now at this moment, but then I want to say something that had already happened:
I'm at work right now. I'm a little late. The last time I was late, my boss told me I would be in big trouble if it ever happened again! My coworker told me that I need to relax and not to worry. So, I'm not gonna worry about this.
