You were all right - things are working out. I think it was just back-to-work nerves. I've been consistently able to pump 12 ounces during my three workday pumping sessions. I seem to get about 4 oz in the morning, 5 oz at noon, and 3 oz in the afternoon.
Yesterday DD only took two of the 3.5 ounce bottles that I sent and she didn't quite finish them - she took one bottle at around 9:30, the next at 12:40, and then they did a craft project : and she napped in the afternoon until I picked her up at 4:15. When we arrived at our breastfeeding support group meeting at 5 she actively nursed for almost an hour. She nursed a ton again at 8:30 and then for a normal duration at 10:30, and slept from 11 PM to 6 AM. That one surprised me!
Her caregivers said that she was spitting up quite a bit with the big 4 ounce bottles, so I won't be sending them that large anymore. I will probably do three 3 oz bottles with an extra 2 ounce bottle in the freezer as a "snack" if needed.
Today she still has the one 3.5 oz bottle left over from yesterday, and I sent in three 3 oz bottles as well. We will see what she takes, but having a little bit of extra milk in the fridge makes me worry less about having enough - especially since we're probably headed into that 3 month growth spurt in the next week or two.