Before you beat yourself up, remember that things don't always go to plan and we must adapt as necessary.
Was the nurse you spoke to an LC? It may be that she's not getting enough milk, or maybe there's something else going on or (very likely) a combination of things. Hope you can get some good advice from the ABA or an LC. Having an LC come to you and getting on top of everything that's going on is probably your best bet.
The best way to build supply is to feed more often. Increasing skin to skin contact may also help, and failing that there are drugs that can increase your supply also. If you can feed again rather than pumping, that is likely to be easier and a more effective way of getting milk out of your breast (more out means more produced).
All the best