It appears as if there's been a misunderstanding. You thought you were being overly accommodating by saying yes, while the other party thought he was being overly generous with his offer. This could devolve into hurt feelings and building resentment if you aren't careful. Nevertheless, it's worth returning to the bargaining table one more time. He's not as averse to renegotiation as you might think. What eventually emerges is an agreement you can both live with. It won't be everything you want, but it's better than what you had—although you'll still believe you're being too accommodating while he thinks he's being too generous.