Ok so I had sex with this girl last nite, I wasn't great on both our parts! Anyway we are gonna meet on Tuesday and I want to txt her saying, 'your staying at mine tomorow, we have unfinished business'! Is that a good idea? And how long should I wait to txt it too her?

Why message it? you're meeting her, just do it in person.

Take her out, have fun, kino, escalate. When its time to get the proper action going just tell her.

"You're staying at mine, we have unfinished business." perfect way to build sexual tension.

Because I need to cement this in, she's kinda flakey, and I'm always choosing where we go, so I thought it would be better just to tell her what's going down!

Bro, you already fucked her. Why are you tripping? If she likes you and is in touch with her sexuality, she'll probably just fuck you again at the end of the night.
This.

annnnnnnnnnnnnnnnnnnd this is what is going to drive her away. Texts like these give off more of a "noone else will have sex with me so I NEED YOU TO!!!" You've already banged her, yeh it wasn't great like you said but you think every girl in the country who are having repeat sex with guys are all having amazing sex? WRONG.

She's invested in you now, she got naked and let you pound her. My first time with my recent lay was drunk as hell. I remember none of it, not even if I came or if she came. Just remember a slight image of her tits. I didn't mention it again just waited.

Next time I saw her, it was at a party. Approached, kino'd then when it got late and she started moaning to me that she was tired I went for it.

Little liar saying she was tired

Your line is perfect for when you've got her up against a wall, just whisper in her ear "we have unfinished business" then fuck the shit out of her.

At the moment she's probably thinking the same as you "oh no I didn't make him cum" or something like that. Your text just validates that it was your fault and that she shouldn't worry = no feelings = less emotional excitement for her.