Pleaseee need advice * supplementing

Tomorrow is my first day at work and I have a bag of frozen breastmilk I just put it in the fridge to thaw for morning.

Right now I don’t produce much so I can only add an ounce of breastmilk to 3oz of formula.

Can I make the 3oz of formula now and put in the fridge and add the thawed but still chilled breastmilk to it in the morning and back in the fridge till I leave?

I need advice 😢

And when you pump at work how do you keep the milk chilled till you get home? I have a bag with insulated front part would that be good with an ice pack?

Advice please!!!