Weight gain concern

My baby dropped from down to a very low percentile after being in the 22nd a few months ago. She’s now in the 3rd percentile. The dr wants her to gain more weight.

She doesn’t eat a lot (less than the minimum 20 oz a day of BM). She eats 3 “meals” a day but small quantities I think compared to other babies. But she’s happy she never seems like she’s cranky due to being hungry ever. Sleeps well. Usually up around 4 Am to nurse.

Anyways, I’ve been stressing about this since her appt trying to fit in extra peanut butter and extra ounces to fatten her up but it’s so hard! If she’s happy and healthy (I guess healthy by my standards, and looks healthy just looks a little younger than she is), would you stress about this? I can’t force more milk down her throat like what am I supposed to do. Any advice or similar situations?