My DD was nearly 7 weeks early and was 2350grams when she was born, dropped to 2170grams and it took her almost 4 weeks to get back to birth weight and she had slow gains for the first 6 months. The she discovered solids and blossomed She was almst 5.5kg at 6 months, so about the same size as your wee one, and she was fine her Paediatrician was happy with her growth and gains. If your Dr is happy and she is developing and having plenty of wet and pooey nappies than I wouldn't get concerned

She sounds as though she is dong beautifully and is just a gorgeous little poppet

Take care
xxoo