guidelines for premie weight gains

Prems who gain 30 gm or 1 oz per day are doing quite well. Sometimes when they're still really new, they have trouble feeding for enough calories when balanced against the calorie expenditure of getting the milk in. The harder they have to work, the slower their weight gain. That's why most NICU/IMCN babies are weighed daily. And why they might need gavage feeds for some time before they get up to speed.

The usual total daily fluid requirement for neonates and young infants is about 150-165 mL/kg.

The baby in your question weighs about 2.5 kg, so let's do the math:
150 x 2.5 = 375 mL/day or
165 x 2.5 = 413 mL/day.

There are 8 feeds in a day at q3h so
375 / 8 = ~47 mL which is ~1 1/2 oz and
413 / 8 = ~52 mL which is just under 2 oz.

So yes, this baby is getting enough to grow.