The worst thing you can do is pile guilt and shame on top of your already many feelings and emotions! There's no shame in having any type of feelings. Feelings are transient, they come and go. It doesn't make you a bad person or a bad dad to be unsure or scared.
Anxiety loves company so the second you feel anxious, then you start to feel anxious about feeling anxious, and it just snowballs at breakneck speed. I went through this exercise just a couple weeks ago, and it seems to happen from time to time especially with so much covid-related anxiety already built in.
I know it's hard but instead of focusing on regret or guilt about the baby and going down that avalanche of negative emotion, try to refocus your brain on the potentially positive things no matter how small. Maybe it's decorating a nursery, or maybe it's how excited your daughters will be to find out they have a new little sibling, really any little thing you can think of. You might want to try keeping a gratitude journal to remind you of all the things in your life that are good. Write down maybe 3 things every night. I think fake it til you make it is a tried and true approach. The more you focus on the bad stuff, the more you'll feel like only bad stuff is happening.
I think this has been done on this forum before but we can start a new gratitude thread where we can all post good things in our lives if that would be helpful for anyone