Obvious I am new to this. If I screwed up this interaction, I would love to learn from it and need advice on how to proceed.

The backstory- met this girl online. Flirty and fun emails. We meet up on a Saturday night. Have a lot of laughs, have a lot in common. I notice I make a few mistakes and looking back there were places I definitely could have amplified things, but overall went well. We text each other the next day, flirty recall some things from the previous night (stupidly have a rapport building convo thrown in-- built off from last night's interaction and she iniated it) looking back I suspect this may have been my own undoing. We text a little bit throughout the week.
I ask her to join me at a friends art opening; she has a work obligation but says she'll try her best.Oh, she just stated a new job this week too. friday comes along, no text no nothing. I say scew it and decide to move on. But in someways I understand why she wouldn't want to go. It was 300 -400 people. A majority of the people I know, and know well-- we've only hung out once before and all that could be too much for some women. I just figured it would be fun because she likes art. Also I don't really make my intentions known. So here is another rookie mistake I need to learn from.

I don't hear from her and decide I won't text her. 5 days passed and I figure I'll text her. She responds 3 plus hours later at 1130 at night.
She says "Haha hey there, sorry i know it super late, I've been working all evening. Bummed I missed the event and yeah don draper was after me:) (a reference to an earlier convo) Anyway maybe we can grab a drink soon I'm off (insert dating website) Life is too crazy right now to manage that thing. Hope youre well and btw my dog ate my book report "

So my question is how to follow this text up. It's been two days since. I've been busy myself. I don't think she is that interested since she threw out a noncommital maybe and if she really wanted to hang out then she would make time. Another side of me says, she responded and she just started this new job and has lots going on.

should my next text say something like I'm busy too but I could do drinks early Friday or you can come along Sunday to something I am already doing and see what she says? Am I overthinking all this?

You're too scared and being too negative as a result. You can't control being scared but you can control being negative about it. Dude if she wasn't interested she wouldn't have bothered with that message. Not after 5 days.

Fortunately it probably all worked out for the best - my guess is, for whatever reason, she was too scared to come - either the thought of 400 people, or something you said or did, or just something to do with her. I think you should have called to see if she was coming, unless you didn't care that much. Anyway, the time you let pass, probably had a good effect. I think you should have tried to contact her beforehand, but sometimes, when she disappears for no reason, and you just give it a few days, it can have good effects. Gives her time to calm down if she had some reasons for disappearing, makes her wonder what you're thinking, gives her her space if you came on too strongly, etc. As a guide, if a girl flakes, and there's not even a slight sign of lost interest, she might detect that you're a bit needy and will put up with anything. This is a very "feeling" based decision and I'm not going to lay down any hard rules about it at the moment.

Anyway, back to the present - you're on. Her text was very informative, she's informing you of things, referring to past jokes, these are all indicating she is coaxing you back.

So just keep going as normal. Whatever you were doing in the past that got her out, keep doing that. Get in a small catch up sooner rather than later (without sounding needy - and that's all in the delivery - you can make a catch up the very next day if you word it right) particularly if there is a cool event you want to invite her to - do a small catch up before then, and then tell her about the big event during the catch up.
Otherwise, think of something to follow up the small catch up with. Either before hand, or find something through your conversation during the catch up. If she's keen she will pretty much give any excuse to catch up, eg. she will express interest in a lot of things and give you chances to mention that thing as an excuse to catch up again. Do your best not to leave it till after you part ways, that's usually bad. At the very least, have something generic as a stand by, movies are always good, or some new restaurant you wanted to try, and drop that idea just as you guys are parting ways.

You don't have to make a "new restaurant" as an excuse. Just have a couple of places in mind, and before you part ways, you can just say for example "Do you like turkish food?" and if she really does say no, you can say "ah - do you like sushi then?" odd's are she won't turn down two in a row, but if she did, wow, that's a joke in itself, you'd say "really?? come on, everyone likes sushi. What do you like?" but anyway, these are all examples. The point is you can just say "do you like X food" or whatever, and then say "Cool, there's this awesome X restaurant, I'm gonna take you there" and then set a date. Then you have till then to think of ways to jazz that night up a bit - never stay at the restaurant, as a bare minimum, go for a walk very soon after finishing, and keep talking while you walk. Moving scenery seems to make time last longer.

But odds are, if you really get along, you won't have to go that generic, something in the conversation will be an excuse to catch up.

wow. thank you so much for the reply. really helps-