My Baby Is 6 Months 4 Days Old.She Weights Only

My baby is 6 months 4 days old.She weights only 6.1 kg.She refuses eat Formula feed.I need to force fully feed her 3 ounce.Now I have started with Cerelac Rice which needs to be diluted so that she can be forcefully feeded.Since I need to dilute it she can take only 2 scoops of cerelac.I even tried to feed her with boiled lentils water(boiled in salt water) but we need to force fully feed that even.Please suggest