You'll get there mate. It's quite normal for your milk to take this long with your first. With my first it took 99 hours for my milk to come in.

Do look up baby led attachment, and see about letting your little girl lead the way with feeding, as it could help.
Do keep looking after those nipples, it's a big adjustment.
Do keep feed feed feeding. It won't be like this forever, I promise. The first few weeks are intense, but your baby will get calmer, and it will all get easier. Every 3 hours is a lot less than either of mine fed in those first three weeks. I felt like I was living on the couch feeding; and that's what tiny babies do to you!

And don't feel guilty about those crazy Day 3 feelings. I sobbed my heart out after DD2 arrived, those exact feelings you described. Ruined my life, ruined my DD1's life, ruined everything. Only now, I realise how much she's actually brought to us, and I laugh about it all.

Hang in there!