My 2months old girl is currently drinking 100ml BM every 2hrs. I personally feels that 100ml formula is too much for a 20days baby & formula is heavier/fuller than BM. When my girl was about about 1month old, we gave about 60ml BM. Perhaps u can try to reduce the formula milk to 60ml or any amount you think it's suitable. Only if baby cries for more, than u give him 100ml.
Fyi, I did not calculate her milk intake by using her weight/number of feeding per day. Some people does that. What I did was we tried with 30ml & slowly increase each week or when she demands for more.
Haida Addellyn Armani