It sounds like you're not feeling very sure of yourself. The ways you describe yourself are quite harsh. I understand you haven't handled this well in the past but there's no reason you can't learn from your mistakes and grow as a person. It seems like you're putting a lot of pressure on yourself. I read something in a book once... loosely paraphrased: "Applying pressure is the fastest way to kill joy, curiosity, and excitement." I think they were applying this to physically intimate intimacy, but I think you can apply this to any part of any intimate connection.
I firmly believe that a caregiver of any kind's first priority is to themselves so that we can provide more wholehearted care to the people we care about. Look at how harsh you're being towards yourself. Would you be this harsh towards your little? It sounds like you've made mistakes in the past and have some pretty big regrets, but give yourself some allowance to be new to this. You're figuring out what works for you and so is she. You'll likely make some mistakes and that's okay. It seems like she's sensitive to how you feel about yourself in the moment, which is normal for most people in an intimate relationship.
Take a breather, give yourself space and grace and you may find that the residual effect trickles down into your relationship. Finding a sense of internal peace means we can offer that peace as a gift to those closest to us. There's been a lot of great suggestions in this thread, but don't forget yourself in this either. You're worth the same loving kindness you want to give her.