Help, I'm in a pivotal negotiation and I'm not sure what to do

First of all, I'd like to thank the Indie Hacker community because I would have never gotten to this point if it wasn't for the inspiration provided by the members here.

I want to share specifics but cannot do so since the information I'm sharing is confidential, so I'll try to outline the situation generally without giving away specifics.

I've been working on a side project for the past two years, on nights and weekends, to build a web application for an online teaching company which I'll call Teaching Company for the rest of this post. I didn't get paid for this work during this time.

Up until this point, they have been using a generic software solution that any of their competitors can use. While it gets the job done, it's not sophisticated enough for their needs, and my software is meant to fill that gap.

After seeing how far the software has come, Teaching Company is happy with the product and wants to go live. We've only made a verbal licensing agreement so far, where we would provide the software for their exclusive use for $5 per customer a month.

Now that Teaching Company is all in on the product, the CEO offered to buy the software. Here is what they offered. Around 90K up front and 4% equity in the Teaching Company.

The CEO expressed that this is a good deal since my software isn't worth that much at the moment and Teaching Company can potentially sell for over 50 - 100 million dollars years down the line. I somewhat changed all the figures mentioned above for the sake of confidentiality.

Here is where my head is at and some important context about this deal. I never had to build software for a single company. There's way more money to be made by competing in the wider market, although it's significantly harder upfront. I made the decision to build software exclusively for Teaching Company because I believe in their product, and more importantly, I care about my work-life balance and having time to spend with my family. With that said, competing in the market is technically still on the table since we haven't signed any contracts yet, and we've only made verbal agreements so far.

Of course, as the CEO said, the software isn't worth very much at this point since it's still in the beta testing phase—but that doesn't mean we shouldn't consider its future potential worth. For the same reason why the CEO may not want to sell Teaching Company right now since it may be worth a lot more years down the line, I'm hesitant to do so as well. Even if we're providing a solution that's exclusively for their use, it's very possible that down the line, when the software matures, we may collectively agree to offer it to other companies and potentially greatly increase revenue.

My gut reaction is that this is not a great deal and I'm still thinking through what would be the best counter offer. How would you approach this negotiation? This is my first time going through this sort of thing and could use some advice. Your feedback is very much appreciated!