TLDR: I thoughtlessly let slip to one of my gf's that, out of all my of partners, I think she's the worst in bed. I've apologized but I still feel shitty and she still feels hurt. Does anyone have any advice on more things I can do to make things right?

I got back home from a hookup yesterday and one of my gf's, who was feeling insecure at the time, asked me if I and my fwb had discussed ranking how good each of my partners was at sex. At some point in the conversation my gf indicated that she was concerned that my fwb was gloating or something like that. I told her the truth, which was that I had briefly discussed this with my fwb the previous night. My fwb had asked where she ranked, and I probably shouldn't have answered but it was sort of casual pillow talk and I was half asleep. My gf was immediately upset by this and I suddenly realized that I shouldn't have engaged with this line of questioning.

Basically, one second I'm casually telling my gf everything about my fun hookup, and then I'm suddenly going "oh shit, some thoughts shouldn't be shared out loud! I should shut my mouth before I say anything else!" I have a long and storied history of putting my foot in my mouth but I at least had the sense not to tell her what the rankings were. However, enough information came out in the conversation that she pretty quickly deduced that she was at the bottom. This understandably really hurt her.

I feel awful about hurting her like this. I wish I could take back what I said. I apologized immediately and we've at least smoothed things over a bit. I've told her how much she matters to me and how I'm still extremely attracted to her. I've made a new policy for myself that I will not provide any rankings of my sexual or romantic partners to anyone. She has promised to work through some jealousy/insecurity issues that motivated her to ask about this in the first place. However I can tell that she's still hurt and feels shaken by what I said.

Does anyone have any advice on things I can say or do to make things right or repair the damage I've done? How do you all manage to navigate situations like this with your partners?

Edit: To clarify some misunderstandings I'm seeing in the comments, my fwb never gloated about anything, my gf was just worrying about it. All my fwb did was ask "Hey, how do I rank among the partners you've had", and then I inadvisably told her, and then the conversation moved on. She never even really directly mentioned my gf.