Feeding on both sides...

So my LO who is 15 weeks always fed on one side and I used the Haaka on the other and she seemed content after so I didn’t think anything of it as she was gaining fine. She ate every 2-3 hours.Well I went back to work and she was taking 4oz bottles. I did a weighted feed for the heck of it and she only took in 2 oz from 1 side in about 5-10 mins. Now I feel horrible n feel I’ve been starving her this whole time! So I’m trying to offer both sides each feed with a burp between. My question is let’s say I start on the right burp then offer the left and she only nurses a few mins on that side.....next feed so u start with the left since she didn’t empty it or start with the right again?? I’m use to switching each feed so I’m not sure! Thanks in advance!