I don't think you can help it really. Milk supply at the start is driven by hormones, not supply and demand yet. I would just keep pumping 3hrly both sides because a newborn would feed at least that much.

HTH
Totally agree and freeze the excess milk. Don't attempt to dictate your supply by pumping and especially as she is so young and a prem.

I had to exclusively pump for 5 weeks when DD2 was 2 weeks old and was pumping around 80ml total initially too. It increased but not significantly and I was pumping 3 hourly around the clock at first then I cut back to 4 hourly overnight. We reintroduced the breast gradually from 7 weeks and then DD worked out my supply for me. The excess was a bonus as I've had a constant supply of EBM in my freezer since

I had to pump with DD1 too and my supply also just worked itself out once DD was back on the breast full time.