As a veteran breastfeeder, believe me when I say that you have to trust your body. You don't know how much they're getting, but the baby will soon let you know if they're still hungry! Your body and the baby will take care of the quantities, it's not something mum needs to worry about. Just feed on demand and you'll be fine.
On day 2 the baby will feed almost constantly. It's not because they're starving or not getting enough, it's their way of telling your body to produce milk. Stay strong because that day can be hard. But honestly, my best advice is trust in your body. It knows what it's doing