I've prepared sweet potato puree mix with bm last night and store in fridge. Can i feed tonight? Im not sure if i am suppose to blend with bm first & store?

Yes you can still feed your LO tonight as long as it was immediately stored in the fridge and not previously exposed. I personally prefer to mix my EBM to puree just before feeding because some puree may get more watery in the fridge (or freezer).