The fact that you pumped 28 oz is great! And suggests that you don't have a "medical" reason for low supply, and that if you pump enough, you will produce plenty. Not every mother gets the "full" feeling, so I don't think that's a good guide. How is baby's weight gain? How much supplement is the "odd bottle of formula"? If baby is getting only an occasional supplement and is gaining well, that means you ARE making enough milk. Which 23 oz may well be. And if you pump more, as auderey points out, you should increase your output. I wouldn't fixate too much on the number 32. That is really on the high end of normal or even above normal, depending on who you ask. I think it's a bit unfortunate that your doctor's office is focusing on 32 and labeling you with low milk supply - because it's making you doubt yourself. You can do this! You ARE doing this! It's great that baby latched 3 times! You will get there. I know it's hard not to focus on the numbers when you're pumping, but really - if you were nursing you wouldn't know how many ounces baby was getting, all you would know is whether baby's diaper output looks good and whether baby is gaining. So those are the things to focus on.
By the way, are you doing hand compressions either during or after pumping? What about power pumping?