Good enough supply/ latching tips?

Sa

Hi! My baby was 3 weeks early and has some trouble latching so I’m exclusively pumping at the moment. I use the Medela Calma nipple so she won’t get used to an easy flow and never return to the breast because I plan on actually nursing again soon. She is exactly one week old today and eats about 2oz every 3 hours. I use a hand pump every 4 hours and get 2.5oz from each breast within 10 minutes but after that no milk will come out. Is that a good supply or too low? And if I use an electric pump will I be able to pump longer? I want to start trying to put her on the boob again but she never opens her mouth wide enough to get a good latch. Any tips on how to achieve a better latch?? I’m fine using a bottle with my milk but I’d really love to be able to nurse her during the day. During skin to skin or if she’s laying on my chest she always shakes her head back and forth and shows that she wants to nurse (we nursed the first 2 days in the hospital with a lot of help from the nurse) but she just won’t open her mouth big enough to latch.