Baby not finishing her bottles. Help!

My 3mo and has been eating a lot less lately and it’s worrying me. From what I understand, she should be getting 2.5 ounces per pound per day. I weighed her today and she was 12 pounds—which means she should be eating 30 ounces a day, but she’s only been eating like 18-20 ounces (down from about 25 ounces a few days ago). She’s been super fussy about halfway through a feeding, and sometimes when we burp her she gets worked up and refuses to finish her bottle. She was a month early and her current weight puts her in the 72nd%ile, which is up from her weight/percentile from her 2mo appointment. Should I be worried? Could she be going through a growth spurt? She did eat a little less when she went through previous growth spurts. Could this just be a phase?