Baby not gaining enough weight

UPDATE: I bought a scale so we could do weighted feeds. He’s eating about 3oz per feed and has gained over one ounce per day. We’re doing it! 🎉 thank you for all your advice!

This is probably a stupid question but my pediatrician told me my son isn’t gaining at the rate they want him to (21g/day instead of 30g/day). He’s in the >1% & fell off his growth curve. He’s 1 month old. She said to feed him every 3 hours for 10 minutes on each breast. That worked for about 24 hours but today we just hit the 2 hour mark and he’s hungry. I’ve always latched him on demand and sometimes he’s 100% comfort nursing, but I can tell he’s hungry because nothing else is getting him to settle. I give him a paci and he spits it out & cries when he realizes there’s no milk coming from it. Anyway, my question is, shouldn’t I nurse him at the 2 hour mark because I know he’s hungry, even though the pediatrician emphasized 3 hours?? (PS I have him latched rn because I couldn’t stand to see him hungry, but I feel like it’s wrong to go against the pediatrician?)