My understanding is: it's fine. You're not required to do follow-on financing. Perceived preferred access to the market for syndicated convertible rounds is a big reason people do YC, though, so I think most people do end up raising.
This is my biggest worry. I'd like to get some help building my stupid golf wiki (which I actually think is an extremely profitable long-term venture), but I'm desperately trying to build something that is good for golf, which is a space notoriously saturated with bad actors. I'm honestly even considering going in a not-for-profit direction eventually, so the idea of applying for a bit of VC money honestly hard to square, but the connections would be what's valuable.
Keep in mind that if you never raise again, YC still owns 7% so they have no reason to complain. If you're successful, 500k for 7% will have been a good deal.
tptacek answered your question, but here's a rule for answering similar questions in the future: YC supports what founders choose. That's partly because it's the DNA of the organization (whose origins go back to a time when founders were much lower on the startup totem pole than they are today) and partly because it's a losing bet to do anything else (which is related).
This is the equity deal: https://www.ycombinator.com/deal
What if I don’t want to raise any more than the 7% (which in itself is $125k I don’t really need but happy to give 7% for the higher P(success))
What if I want to bootstrap from that point or at least keep options open?