If I pump out my bm on the 1st and kept it in the mini fridge, can I still feed my LO? It's already 4 days

Mini fridge means not frozen. I wouldn't as it was 4 days ago. My 'fresh' milk didn't last more than 3 days and anything longer than that, I would put in freezer. I would suggest u to use the milk to do other things like bathe LO instead of drinking. If in doubt, better not let LO drink coz their immune system is not as strong as ours yet.