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

if not froozen i recommend not to give as bacteria might be dead. And for mini fridge temperature might not be cold enough to store the breastmilk and afraid it might not be fresh. So play safe of baby health do not give. U can use the milk for other usage such as bathing if not you got to discard and waste it.