It sounds like you didn't do enough to ramp up her attraction for you.
Most likely because you didn't speak and behave in ways that were attractive enough to her.
Teasing, flirting, having fun, being joyful, positive, enthusiastic, displaying mental and emotional strength.
For example, you could have come over as more attractive when you apologised and said to take it slow.
It would have been more attractive if you'd disagreed with her in an amused tone of voice. And said that you prefer women that are decisive, that don't play the "let's take it slow" card. As in the past your type of woman has been bold enough to co-operate / be comfortable with the sexual side of things by the 4th date. And that you're starting to wonder if you should friendzone her as a result.
By telling her that you would have come across as honest and mentally and emotionally strong and selective by being prepared to relegate her to being a friend in your social circle.
By apologising and agreeing with her frame you came across as weak and possibly unauthentic.
Another possible tactic you could have used, would have been to tell her straight away - in a gentle / amused / we're enjoying each other's company / mock serious but not serious / I like you tone of voice - after she nearly bit your face off that she was moving too fast and you'd prefer to slow things down (enjoy the process of getting to know each other). In that way it wouldn't have been her coming to you saying that you're moving too fast. Because you'd have already said it.