Mother's own milk is always preferable rather than formula.
Yes, you can preserve pumped milk for 4 hours at room temperature itself, and 4 days in the fridge.
Next Steps
To maintain the breastfeeding,do the following:
Lots of skin to skin to keep baby calm
Pump atleast 8 times a day, half hour before breast feed.( this will help to express your milk,and also draw out a flat nipple)
Try nipple shield to latch baby
Give expressed breast milk by pallada, avoid feeding bottle.
Health Tips
Meet a lactation consultant in person or online for more support.