Weight Question

My daughter's birth weight was 3.7 kgs. That is 8 lbs. that's above the 77th percentile(according to the glow home page growth charts). Then she dropped down to the 65th percentile then 51st percentile then Now at 15 weeks she is in the 61st percentile (weight). She did regain her birth weight and more at 10 days after birth and she is an exclusively breastfed baby. I'm an FTM, I'm wondering are babies supposed to maintain their birth weight percentile? Is her drop not ideal? Was she always supposed to ideally be in the 77th percentile since that was her birth weight percentile? Pls enlighten! I'm wondering if my breast milk is enough and concerned as she dropped from 77th % at birth to 61% now.

She hasn't been sick or anything for the weight drop. Hence the doubt that whether my breast milk is sufficient and healthy for her. Sorry about the long post ....