Friendship with an ex partner is so much easier said than done though - especially only a few months on when you are still hurting from the relationship going wrong and grieving for a future that you thought you had together. It takes time to recover from all of that and trying to maintain a friendship whilst you get over the relationship can be really unhelpful for your recovery, in my experience and opinion anyway. That's not to say friendship with an ex isn't possible - but for me it was possible a year or so after the split, I needed the time apart no contact to move on with my own life.
I understand that there is a parenting relationship between him and your daughter as well to consider - is he planning on maintaining that for as long as she needs, as she grows up, the next 15/20 years? If so, I'd suggest at least temporarily formalising your relationship to only contact regarding arrangements for your daughter. Otherwise, I'd really recommend no contact at all for an extended period 6-12 months at least. After that you can pick up a friendship without all the raw hurt and grief you have now.
Has he responded at all?
Either way, my advice now would be to write to him again, explain that you regret sending what you did and do not wish to discuss it further, and set your new boundaries (no contact for X time or contact only regarding arrangements for your daughter, if he plans on remaining in her life LONG term) and ask him to respect those boundaries, as that is what you need to heal.
Hope that helps and that things look less bleak in the light of day 