6 week old transferring 2 oz a feeding

So long story short I starting breastfeeding exclusively week one with my baby and he kept losing weight because he wasn't transferring enough from me. He was 3 weeks early and I have flat nipples so we were using the nipple shield. I started pumping and supplementing him with breastmilk through a bottle on top of nursing with the hope he would improve so we could switch back to just breastfeeding. We have improved and I have ditched the nipple shield but when we did a pre and post weight he got about 2.3 oz from me after about 40 minute feeding. Is that "normal" for a 6 week old or should he ideally be getting more? I'm just nervous to switch back to exclusively breastfeeding and him not get enough from me.